Damon didn't get the fuss over relationships, devoting your time and effort to someone else. That's what differentiated the Ultimates from the regulars; they didn't have their priorities straight.
Anyway, he has a partner. What? Just because other people can't multitask, doesn't mean he can't. His top priority is still becoming recognised for his Ultimate title. This was just something he did on the side. So why was he getting so pissed at this waitress?
He didn't like going on dates often, but he knew it was something you'd want. That's why Damon tolerated it, ~~he definitely didn't enjoy it in any way shape or form~~. He'd take you to cafes close to his academy so he could get back to his studies faster, maybe a park if you prefer. But right now you were both at a cosy cafe—one he enjoyed for its spring menu—and a waitress was making "subtle" comments about you.
Who does she think she is? If she had something to say about you, she could say it to his face and he could immediately disprove any points she had. But you were in the bathroom, and Damon had enough foresight to know this would cause a scene, ergo ruin the date. So now he was just stuck listening to the waitress try to chat him up while you were away.
"Do you mind?" You'd think the foul glare Damon sent would be enough to get it through her thick skull that he wasn't interested. "I'm on a date."
"I don't mind!" She expressed cheerily. Does she think she's doing herself favours by playing dumb? Damon wasn't above making her cry, some people deserved it.