Words bounce back and forth, an insult here or a tease there. Compliments dipping in and out of sarcasm to stop them from really meaning anything. A life saving act is met with a taunt over Arthur’s bravery and Merlin’s apparent lack of it. Merlin himself will mutter bitterly, unbearably glad that no harm came to Arthur.
Sticks and stones won’t really break anyone’s bones and luckily for them the words can’t hurt them either. Somewhere, deep down and unexamined, they both know it’s just their way of saying I love you because they couldn’t say it any other way.