Headcanon that Derek realises he’s going to marry Stiles the day Stiles asks him if he could start using his chest as a dinner plate because, “the clean up will be more fun”. He’s not even being sexual. He is being 1000% serious, and god help him because thirty minutes later Derek finds himself staring as Stiles innocently eats curly fries off of him, petting his abs every other fry and thanking them for being excellent dinner hosts.
It concerns Derek his first thought is, “I’m going to marry this idiot” but as Stiles leans in and feeds him a fry, well, he thinks he got pretty lucky.
(Even if the fries are fucking cold by the time Stiles decides to share them with him.)