Harry tips his head back, and Draco's tongue invades his mouth -- it's always an invasion, like something unwelcome, even though it's not. Or it shouldn't be. At this point, Harry mumbles, "fuck, Malfoy," and Draco doesn't know if it's the impersonal use of his name, or the casual throwing out of 'fuck' that turns him off. He detachedly feels himself flinch, violently enough that his lips fall from Harry's, and instead of trying to reinitiate a kiss, he touches the back of Harry's neck and tilts forward so that their foreheads touch. He feels the tension flooding out of his body.
Harry likes to talk dirty; Draco hates it.