For me, it's Ignition by R. Kelly. When that song comes on, me and one of my mates sing all the words and just don't stop dancing for its entirety. It sort've started as a joke years ago, but now I love it! Oddly enough if I'm not with him I don't particularly care about the song, but when we're together it becomes the greatest song ever. I love it.
Do you guys have a song that when you're out and it comes on, you just love it? Or maybe request it whenever you're out?