the yr 12s as their end of school thing did this, a couple of weeks ago.
7 guys lined up, wrote 2 0 0 & S E X one letter on each of their backs, then took all their clothes off, and had a photo taken that was then up all over the school.
all the girls got pissed they were being outdone, so they did the exact same thing.
so you would walk around, and there would be yr 12 arses on the wall...
then all the guys started stopping and starring at the girls ones, trying to guess who each one was just from the back view. was gold.