That’ll do, pig. That’ll do.
Yup 
There’s also:
. . . those who eat quiche?
SAVE RUSSIAN JEWS, Collect a whole set! 20 years ago when the thing was going on.
Some people come here to shit and stink,
Others come here to sit and think.
I come here to scratch my balls,
And read the writing on the walls!
(written diagonally across an urinal) you are now peeing at angle of 45 degrees.
SAVE SOVIET JEWS!
Win valuable prizes
There are only two types of people in the world: Those who think there are only two types of people in the world, and, those who know better.
“All you need is love, All you want is sex, all you have is porn!”
Written on condom dispenser, “this is the worst chewing gum I have ever tasted”
At my very first college, there was a small lounge deep in the heart of the science building - couches, vending machines, restrooms. My friends and I, none of whom were science majors, used to study in empty classrooms at night, and often took study breaks in the lounge, which was called The Nucleus. Potty breaks, too, and I - being an English major and a liberal arts snob - once wrote that judging from the essays on the walls, half the science majors at my college were failed English majors.
The next night, someone had responded, “Correlation does not imply causation”. I had to look it up to figure out what that meant.
“Overpriced too”
This was such a fun thread I’ve decided to resurrect it.
Any additions?
Heisenberg may have been here.
Here I sit, reading graffiti.
This fuckin’ stall’s all out of T.P.
Long ago, in a bathroom used by both bikers and Japanese bike riders, one of the bikers drew a massive rising sun over the urinals, overlayed with the words “REMEMBER PEARL HARBOR!” Down in the corner, I wrote “Yeah, they won.” Three days later they painted the bathroom.
Over the urinal at school:
“Why bother looking up here, the joke is in your hands”
Best example I’ve actually seen “in the wild” was in a college dorm restroom. In response to a rather mundane
NUKE NIGERS
was this geography lesson:
Niger is a country in Africa. It’s also a river that flows through that country. There really isn’t much there worth nuking.
Specially for Nigel Powers, from a Leiden University loo, bathroom wall poetry in Dutch: “Wie zijn string niet op tijd laat zakken zal zijn poep in tweeën kakken.” Roughly: “Those who do not drop their thong in time will crap their shit in two.”