There are a lot of arguments Harrison has running through his head, like the fact that Felicity has never once tried to have a normal conversation with him, or that bothering him is not the same as just trying to talk to him, but he's so struck by her comment about making out that most of that flies out of his head.

"Why the hell would you expect that?"

Despite asking the question, he doesn't actually wait for an answer - he essentially throws his hands up and starts to walk away. He needs a smoke or something. He can tell she feels a little bad but... he doesn't have time for this. And it's not his responsibility.