Over the Weekend

I was introduced to my brother's girlfriend's co-worker, an attractive and friendly 28 year old from Dallas. Not five minutes after the introduction, some guy who knew somebody in the group we were hanging around comes up to me and says "I got a mission for you, Brian (he mixed up me and my brother's names a number of times)."
"Joe."
"Whatever. I want you to stop acting so nervous and start talking to ever girl here but that one." He pointed to our co-worker. "Then, talk to her like it's no big deal. When you're fucking her at the end of the night, you'll have me to thank."
This struck me as a faux pas. What if I had come out and said "Pardon me, that's my sister," or "Sorry, friend, I'm gay." I imagine he'd have been red-faced then. Or, what if I said, "Already did last night, bitch-ass..." I really can't tell which one was on this fellow's level.