Speaking of not seeing things yourself, q.v. post #19. 
I like the interactive ones.
In tiny, tiny print at the bottom of the stall door: “you are now shitting at forty-five degrees.”
On left wall of stall: “Want to watch toilet tennis? Look at the other wall.” (repeated on right wall of stall)
Dang! Missed that!
In the 6th form canteen at my old school, there were a couple of memorable sayings on the wall. The first said :I have seen the Great Pretender
… but he is not what he seems …Close to that was the deeply philosophical statement (well, for 16-year-olds)Even nostalgia is not what it was.
In the men’s room at a pub near my house, I once saw the following missive.Sue, if you ever read this, we’re through…
But my all-time favourite, from a collection of same I acquired while at Uni :Abandon Hope. Pandora took the money…
Many years ago - mid 70’s, the fieldhouse at the University of Chicago was essentially nothing more than a big building with some bleachers and a red clay track. They held AAU meets there a lot that my coach would take us to run in. You’d ride home blowing nasty red snot, but I digress…
In the downstairs men’s room, I saw this and never forgot it:
“Dickie Nixon took his wife to see Deep Throat 5 times before he finally got it down Pat”
In the 80s, somebody had written “LOOK WHAT LABOR (the party in govt at the time) HAS DONE FOR AUSTRALIA!”
But they wrote it in a gay precinct, and before very long at all, it had been changed to:
“LOOK WHAT GABOR HAS DONE FOR AUSTRALIA!”
Ah, but there’s verse 2:
Yet far better this
than to take a chance
Try to fart
and shit my pants
I don’t remember whether I saw this on a bathroom wall or Mad Magazine but here goes:
Those who write on bathroom walls
Make their sht in little balls
Those who read these lines of wit
Eat the little balls of sht.
Written over the urinal:
Stand closer - quit bragging
Regards,
Shodan
One of the most famous pieces of UK graffiti was this one.
And I remember seeing a load of original Banksy pieces as a student in Bristol back in the late nineties… this was one of my faves.
On the fourth floor of the journalism building at UGA, second stall from the south door, there is a theological argument that takes up almost the entire left wall of the stall. Some of it is very well written, some of it is just name-calling, but it’s amazing that the whole damn wall is filled with people arguing over the nature of god. At the very bottom, slashed in all capital letters with a furious sharpie is the sentence “CAN’T YOU PEOPLE JUST TAKE A SHIT AND BE DONE WITH IT?” I cracked up the first time I saw that, and I sure hope it’s still there.
Then there’s a nonsensical one over the urinal at a restaurant in Athens that I love that says “Matt is a gay mathematician.” Makes me chuckle every time.
I should also mention (okay,maybe I shouldn’t, but I will) the four toilet stalls in one of the dorms where I lived at Oklahoma Baptist University. They were labeled 1 John, 2 John, 3 John and Revelation.
Don’t know what happened to Jude.
Hand dryer graffiti: Press Button. Receive Bacon.
‘I may not go down in history, but I went down on your sister’
T-Stand, eastside
Could have been worse. I’d hate to use a stall labeled “Acts”. Or worse, “Lamentations”.
Genesis and Exodus would be cool. 
Near the University of Arizona in Tucson there is a building that has “HAPPINESS IS SUBMISSION TO GOD” printed on the side in huge letters. Directly following the word “GOD” is a patch of discolored paint, from all of the times they had to paint over people putting “ZILLA” after it. It’s an ongoing battle.
I’m rather fond of this one
That reminds me of my friends who are making a model train station for the Spinespur miniature game. For that particular game they need a postapocalyptic look.
Well, it’s going along pretty well except that there isn’t any graffiti yet on the stations name: “CANAL STREET.” Not that it would be funny per se to have the “C” crossed out in their miniature train station, but it would break the verisimilitude to think that no one had done so yet.
Since this might be displayed in a public place, I’m going to suggest that they make a metal “C” to bolt over the existing “C”, to imply that they have to replace it a lot like in your example.
Oh, and for awhile, I think Pennsylvania had a supply of metal "N"s to place over signs for the “DEVON” exit when people kept spraypainting over it.
In the town where I went to high school, there was a college that, quite idiotically, named a men’s dorm after an old alum. It thus became Shorney Hall.
You can imagine how quickly and how often the S was painted over, taken down, taped over, etc. I think they kept replacing it for a few months, then decided to hell with it and it went back to being North Men’s or some such. What the heck, the old alum was doddering; he’d probably never be back to see what happened to his namesake.