It’s not planned, that’s what he’s trying to say.
No, when Crowley first kisses Aziraphale after 6,000 years (give or take) of pining, it’s not the result of some well thought out decision wherein he decides to finally show the angel he loves more than anything else in existence how he feels in no-uncertain terms, and to hell-heaven-somewhere! with the consequences. It doesn't happen during some terribly cringe-worthy romantic moment where you can practically hear violins surging to life in the background.
It doesn't happen after some very mature and adult discussion about the feelings they both know the other has been harboring for ages. It doesn't even happen after they've spent a long night drinking enough alcohol to put down an elephant, and thereby giving Crowley a decent(ish) excuse for what amounts to a completely out-of-character move on his part.
No. No what actually happens is that when Crowley slams Aziraphale up against a wall in the middle of a hallway at a former-Satanic-hospital-turned-paintball-complex to express to him how very not nice he is, his hindbrain, forebrain and all other portions of his brain, decide that while denial has been a lovely place to reside for the previous six millennia, they are rather due a relocation at this point. And “Oh! Would you look at that! Here’s the oh-so-very soft mouth of an oh-so-very-beautiful angel right in front of us! And all we have to do to get there is to just...lean forward an inch. Less than an inch, in fact! How fantastic!”
And so they do. Lean forward that is.
Which is how Crowley ends up pressed - full-bodied - against Aziraphale, hands clenched tight in the lapels of the angel’s favorite coat, while his rebellious mouth tastes Aziraphale’s lips for the first time. Almost immediately after this contact begins, Crowley’s collective brain-parts short-circuit from a combination of unadulterated elation and complete and total shock when Aziraphale groans into his mouth; the angel’s body going lax in Crowley’s grip as he presses impossibly closer to the demon, parting his lips and swiping his tongue against Crowley’s with what can only be described as absolute abandon.
From there, one of Aziraphale’s hands works its way up into Crowley’s hair, where it tugs down on the short strands to draw them even tighter together. The rippling sensation the action has on Crowley is rather like an earthquake, what with how it makes his knees shake and his entire body feel like he’s no longer standing on solid ground.
Luckily for Crowley, there’s a rather strong - and determined - angel in his arms willing to pick up the slack. The arm that’s not sunk in Crowley’s hair slips around the demon’s waist to cling to the fabric at his back, holding them together, while his mouth - his mouth! - does heretofore unknown and delicious things to Crowley’s.
The multitude of sensations the enthusiastically reciprocated kiss produces in Crowley, both physical and emotional, makes Crowley’s head spin, increasing the feeling of vertigo to the point that he’s forced to brace a hand against the wall beside Aziraphale’s head so that he doesn’t collapse onto the angel, while his other hand finds purchase somewhere in the vicinity of Aziraphale’s waist, and hip.
It’s in just such a position, when - as Aziraphale’s teeth nip at Crowley’s bottom lip with absolutely no concern for the way the subtle suction further impairs Crowley’s relationship with gravity - they are interrupted by an altogether too loud clearing of a throat mixed in with an amused guffaw and the tinkling sound of a giggle.
This horrible, horrendous sound results in Aziraphale putting an end to the kiss - but not the embrace itself, for which Crowley is grateful- to address the rude individual responsible for breaking up the moment.
Somehow Aziraphale manages to make words , he even - so far as Crowley can tell - produces sentences in the general direction of the intruder. Meanwhile all Crowley can handle in the wake of the kiss is dropping his face into his angel’s neck and drawing in several chest-shaking breaths of air in an effort to get his body - and his brain - back under his direct command.
By the time Crowley’s able to drag his head to a more vertical position, resting his forehead against Aziraphale’s in deference to his neck, which still doesn’t quite want to work properly, the intruder is gone. Which is just as well, as Crowley’s not certain what he would have done to them if they weren’t.
The look upon Aziraphale’s face as his angel meets his sunglass-covered eyes is positively beaming; and too tempting by far. What with the flush adorning his pale cheeks and those delectable lips still wet from their kiss. It’s only the fact that Aziraphale opens his mouth and speaks that keeps Crowley from giving in and kissing him again. “Hello, my dear.”
Aziraphale lets go of a light chortle at Crowley’s decidedly non-verbal response. Any other day, any other situation, and Crowley might have responded to his angel laughing at him with a bit of witty banter, or gentle ribbing of his own, but seeing as how Crowley still hasn’t managed to convince his lungs to resume regular breathing patterns, he’s out of luck at present.
Aziraphale continues on, unfazed by Crowley’s continued inability to speak. “Well, that was rather...unexpected.”
The words are soft, let loose on a light breath of air that skates over Crowley’s lips, sending another wave of tingles down his spine. He pulls his eyes upward, away from the angel’s mouth to meet the angel’s gaze, and finds the corner of blue eyes crinkled with a smile.
Crowley forces air up and out through his windpipe, his voice raspy like he’s just spent decades wandering a desert with no water. “Bad unexpected, or…”
“Oh, no! Not at all, my dear. The opposite, really.” A gust of air escapes Crowley at the verbal confirmation. In response to his not-at-all-subtle indication of relief, Aziraphale presses his forehead against Crowley’s in an affectionate sort of nuzzle that makes something strange and fluttery take flight within Crowley’s chest. “But...I can’t help but feel like this may not have been the best venue for such an...um...activity?”
The question jars Crowley back to reality, and - with some reluctance - he draws his head away from his angel’s to glance back at their surroundings. The sound of gunfire echoes in the courtyard outside, along with the distant sound of sirens fast approaching. His brain comes back online bit by bit as he recalls where they are, and why.
“Huh. No. Right. The Antichrist. Got to...stop Armageddon, and all… that?” The statement comes out of Crowley like a question, for all that he knows it really isn’t. Because they do need to stop Armageddon. And the longer they delay, the harder that will be to accomplish.
He’s just...finding it difficult to be concerned about it specifically at this very moment.
Despite the mutual acknowledgement that maybe - perhaps - this was neither the time nor place to have engaged in a session of snogging 6,000 plus years in the making, neither of them make any move to part ways from the other. Instead, the hand Aziraphale had lodged in Crowley’s hair slides down to cup the back of his neck, the tips of his fingers moving in tiny strokes through the little hairs at the base of his skull and gliding against his bare skin.
Crowley whimpers at the touch. The hand he still has at Aziraphale’s hip curls tight into the cloth of the angel’s slacks, holding on for dear life, and his head tilting back towards Aziraphale’s. “Angel, sweetheart, if your aim is to get us to stop, you’re going about it the wrong way.”
This close, it’s difficult to make out the expression on his angel’s face, but not impossible. What he sees makes that internal fluttery feeling become a veritable storm.
“Maybe, you could, just this once…?” The corners of Aziraphale’s mouth tilt up at the question, in that 'we both know that what I am asking is technically - by angel standards at least - wrong, but if you don’t actually make me say it, than I can continue to deny utilizing the powers of a demon for my own personal gain and pleasure, and you can claim that you are simply attempting to corrupt the poor unsuspecting angel, so please be a dear and do this thing for me, would you?’ smile of his that Crowley positively adores. And because Crowley knows him as well as he does, Aziraphale doesn’t actually need to say anything to get him to do his bidding.
Crowley will happily do it for free, any moment of any day.
And so, with no further dramatics or discussion, Crowley pauses time around them. He pulls back the hand that he’d been using to brace himself against the wall, and cups his angel’s cheek, stroking his thumb down and over the side of his mouth, thrilled to have permission to touch. “Can’t hold this for long, so we better make the most of it.”
Crowley can feel Aziraphale's smile down into his bones, even before their lips meet again.
Though it feels much better once they do.
 If one can define “happens” to mean “something that has occurred following 6,000 plus years of contemplating, pondering, imagining, fantasizing, hoping-for, wanting-desperately-with-their-whole-entire-being-without-any-hope-of-actually-having-it-occur (also known as pining),” then yes it did - in fact - just “happen.” [^]
 This is a lie. Crowley had, in point of fact, spent the past several millennia perfecting the art of not kissing Aziraphale whenever his hindbrain, or his forebrain, or any other part of his brain, body, or demonic soul wanted him to. He rather felt that he was the world’s foremost expert at not kissing him at this point. [^]
 As this was a rather regular event, Crowley has had ample opportunities to perfect such an art. [^]
 This is also a lie. [^]
 This is less of a lie, but also not exactly true. But, given that Crowley is a demon, he’s permitted one or two dozen self-indulgent lies every day. This particular event was causing him to run through his allotment rather quickly. [^]
 Lying! [^]
 If asked directly, Crowley would deny any sort of emotional response. Unless it was Aziraphale doing the asking, in which case, he’d promptly turn into a bumbling stumbling lovesick fool and be happy about it. [^]
 Not that that would be a bad thing, mind. Just not quite a good idea given their current location. [^]
 Shuddup. [^]
 Crowley can tell very little at the moment, as the portions of his brain responsible for processing things like language and rational thought have departed for greener pastures. Meaning they are busy revisiting the abruptly ended kiss on an infinite loop. [^]
 As both Crowley’s body and brain (as well as all the somewhat more metaphysical/occult aspects of his person) are of the firm opinion that kissing Aziraphale is something that they should continue to engage in for the foreseeable future, this is a failure. [^]
 How long is eternity again? Feel free to round up. [^]
 He is certain that his angel wouldn’t like it though. [^]
 This is not a comparison made lightly, as Crowley has - on occasion - had such an experience. It involved a half-dozen angry boars, a pair of world-weary camels, a basket of rotten figs, a poorly drawn map, and one exasperated angel. Don't ask. [^]
 SIX. THOUSAND. YEARS! Can you blame him, really? [^]