One I always found crudely amusing was a note that said; LOOK DOWN HERE! Then there would be a loooong arrow pointing down to the bottom of the stall wall. Then when you did "look down here" the note would tell you: YOU'RE NOW ****ING AT A 45 DEG. ANGLE.
In one of the restrooms at the U. of Illinois, I noted someone had made a heavy philosophical statement about at arm's length above the occupant's head. He obviously expected a response, which he received....each entry was dated and often initialed. The entire wall was nearly covered with entries that dated back 3-4 years. Some were even repeats, the same writer taking exception as much as a year later to something said following his last statement. A few years later, my wife and I visited her cousin in summer classes...working on her Phd. While there, out of curiosity more than need I visited the same restroom to see what had transpired. Lo and behold, most of it was still there, now dating back at least 5 years or more. Upon exiting the stall, I realized the rest of the stalls had been painted over except that one. I guess the maintenance people were curious as where all these profound statements would lead.

I wonder what's on the walls at Harvard!?!