This is my favorite way to troll, I walk around a mall or something humming a song that is impossible to get out of your head really loudly. One time I stood up in a food court and started singing carol of the bells in A capella. I sat down after about 40 seconds with everyone staring at me and continued to eat my ice cream. About 2 minutes later some guy yelled at me F**k you donkeyhole, now that song is stuck in my head!. Sometimes I walk up to random people at their tables and sing "I'm sailing away" At that point I slide on my heels a few feet away and then walk off. This more often than not results in angry people. Sometimes my trolling doesn't work out as trolling however. One time in music I replaced a kids track with "Never gonna give you up" and everyone started singing.
Still funny, not trolling though.

I'm an ass aren't I?