Bruce wasn't quite sure when he started to equate blueberries with comfort food.
Okay, no. That's at least partially a lie. He did know when he started to equate them with comfort (pushing and poking, and unafraid, and asking his opinion like it had merit, and getting between him and someone else, and casually offering him food, casually sharing). They reminded him of being listened to, of being someone's ally. Of, perhaps, the breaking of bread, with someone who knew, and shared with him anyway. Bruce knew why they spoke to him of comfort.
What he didn't know, is when it started to become a habit.
Not one he publicised, of course. If Tony ever found out, he would never live it down. One only had to watch Tony with Pepper, or JARVIS, or, in fact, anyone, for around five minutes, to realise that. If Tony ever found out, he would be unbearably smug.
So Bruce kept it hidden. More or less. Which was bizarre, he realised, hiding shiny foil bags around the lab like they were the great big bag of weed Tony theorised was his secret (which he tried, actually, but barring the aborted search for a cure, Bruce wasn't really a fan of self-medicating problems away). Bizarre and weird, and so childish Bruce wasn't actually sure what to do with himself, sometimes.
There were other, more subtle ways, of course. The easiest of which was tea. For some reason, everyone expected him to love tea, and blueberry tea was ... Alright. Blueberry tea was actually fairly foul, but then he never actually drank the stuff, he was in it for the smell.
(And, admittedly, the sight of Tony attempting to drink it under the mistaken impression that Bruce was talking about the cocktail, and spraying it across half a room - the tea might be a comforting memory for an entirely different reason, by this stage. Nothing cheered you up like the sight of a damp Tony Stark wiping his mouth and glaring at you like you just murdered his kitten ... robot? Except Tony was more likely to actually kill for that than glare. Anyway).
Bruce wasn't completely sure who he thought he was fooling, though (hiding packets around the lab, when JARVIS was essentially the Tower's Big Brother, or draining cold tea down the sink and avoiding Pepper's faint, sympathetic smile). He wasn't even sure why. There were only so many times you could sneak around hiding your snacks like you were back in kindergarten before you started asking yourself pointed questions. Mostly along the lines of how is this my life? Or, more crucially, when did Tony Stark start looking like the sane one in this partnership, and why has the universe not collapsed yet as a result?
That was the point where, Tony Stark or no Tony Stark, bizarre comfort food or no bizarre comfort food, you actually had to stop, and get a hold of yourself.
And then, watching the strange, soft expression on Tony's face when he started finding them, the complicated little smile and confused waggle of eyebrows when Bruce offered him one instead ...
Alright. Bruce knew exactly when, and why, he'd started equating blueberries with comfort food. With Tony, with friendship, with the small, soft smile on the man's face.
What he wanted to know ... was when, and why, Tony apparently started equating them with the same thing.