As someone who is currently living on campus at a university, I end up using a lot of public restrooms. And quite often, people have written on the walls. Now, I'm sure you can imagine what most of the stuff is, but every once in a while I come across a few gems. For example: 
 
"Chrono Trigger is the best game ever." 
"This is the worst graffiti ever." 
"Like!" 
"But is the like for the OP or the graffiti disparagement??" 
 
People conversing about Chrono Trigger. Doesn't get much better than that.  
 
Now, someone else misspelled the word definitely (he put "definately"), and someone else decided to correct the person by not only putting the correct spelling, but by also putting a trick to remember how to spell it:  
 
"De-fin (like a fish) it, Ely! (A name) "  
 
Wise words, from someone with too much time in a restroom.  
 
So, anyone else out there come across anything good whilst staring at the walls of restrooms (or anywhere)?