Casual acquaintances

I really don't understand how the whole system works. Here is my case in point: I like to get drunk on weekends and it used to be that when I would see someone I recognized (whether or not I actually knew the person) I would shout, "Hey, I know you!" and would proceed to tell them how I know them, ask their name, major, etc. We'd probably have a conversation. The next time I saw this person sober I would look studiously at the ground as they passed and after a few months, most of the awkwardness would have dissipated. I've recently developed an even better method, in which I never speak to people that I expect to see again when I'm drunk. It requires more self control than I usually exercise when wasted, but it is worth it to not have to deal with the soul-crushing awkwardness of the next meeting. Unfortunately, this past weekend I was accosted by someone from a class of mine. "Hey, I know you!" he said, and of course I responded enthusiastically, "Yeah, you're in my genetics class!" "You sit right in front of me!" "Yeah!" So on Monday, there he was, right behind me. And before I had a chance to begin the studious ignoring, he asked how my weekend was. Damn. So now every Monday, Wednesday and Friday I can expect to see this guy, whose name I do not remember, and apparently some sort of discourse is expected at each meeting. Should I comment on the weather? Does anyone actually do that? He sits behind me, so I have to turn to speak, but being turned when there is nothing being said is stupid. Once I've returned to facing forward, if class still hasn't started, can I put my headphones back in, thereby preempting any continuing conversation, or is that rude? I really just don't know. While lamenting this to friends during the commercials of Jeopardy, they made fun and said that I should be happy to have a new "hey buddy." A hey buddy is someone that you do not know, but you say "Hey" to them when they walk past. You never think of them except for at this passing, or, if you're me, when you're agonizing over what pleasantries you should exchange the next time you are confronted with this person.
So please, if you recognize me at a party, don't approach me. I am incapable of normal casual interactions.