The painful slap in the face one receives when they lean too far over the subway track to see if the train is coming. The subway comes... and they are slapped in the face by the train. Not hard enough to knock off their head, but just hard enough for it to be considered a Train Slap.
Me: " You better step away from the tracks, Katie, you're in for a painful train slap."
Katie: " I've been train slapped before, and I won't let it happen again"
A 6+ person slap, where 1 person holds the slap-ee and 5+ others run at full speed behind each other, slapping the slap-ee one after another, acting like train carriages behind the first person. This is done most effectively when the slap-ee's head is held firm so they cannot shy away from the on-coming hands. A Train Slap is usually called upon when somebody has done something wrong and deserves severe punishment.
Guy 1: Dude?! Did you hear that Matt got an 8 person Train Slap for hitting on Marc's girlfriend?
Guy 2: Awwwww dude! That woulda' hurt like sheeeeeeet.
A type of slap created by a girl that went to my highschool. It was named for her because someone would say something so stupid that she would wind her hand back and before the person recieving ever saw it coming it had already hit them. Usually leaving a large red mark on their face.
Dude, you got train slapped! you must have said something pretty stupid.