Tough question! I've made SEVERAL great trolls both with friends and solo. I'd have to say Battlefield 3 though. My friend was trapping another guy in a corner, then I came along and trapped them both in. I then let my friend out but the other guy? WOLOLOLOL No. Also on BF3, this guy went out of bounds and that area was only accessible by climbing over the debris. We trapped him in there and waited for him to get killed by the countdown. Also, there's the good ol' spawn beacon. I placed it in a corner and trapped them in. Good stuff.
An honourable mention is Black Ops. These guys invited me and my friend to a 2v2. We just kept switching to their team and then when they switched teams, we'd switch teams again. We'd just keep coming up with excuses as to why we did it for example: "You got pissed off when we switched to this team, so we thought you wanted us on this team!" and "You took so long to change to the other team so we thought you wanted us on this one!" Great times.
Anyway, what's the worst game you've ever played?