I recall this one from the restroom in junior high where they had recently painted over all the old graffiti:
They paint these walls to erase my pen,
But the shithouse poet strikes again!
*
(Name of boss) is so nasty, he has to sneak up on his dick to take a leak!
BOOKER!
Here I sit
Against my wishes.
Tried to fart,
And shat my britches.
The guy who leave bible tracts in here is a Privy-vangelist.
Stand close, it’s shorter than you think.
I know it’s basketball season, but a guy who dribbles that much should sit down to pee.
GOD SAVES!
But Gretzky scores on the rebound.
God saves? cite?
[hijack]I just sat in pee! :O[/hijack]
Preview is your friend!
Mario is waaaay better than Gretzky.
His4ever refuses to admit that there was a score
Gotcha Ya!
= If you can read this you are too close to the porcelaine =
ôô Hey Jude, don’t be so sad
They didn’t name one after yer!.. ôô
Jake? Who the heck is Jake?
- Rue.
Don’t hover; the eels will get you!
All your BMs are belong to us!
When come back, bring cow pie.
Schindler’s list didn’t say, “Hi, Opal!”
Heh, heh. “Member.” Heh, heh.
on the walls of the SDMB port-a-pottie:
If you close the seat on this little chair
when you’re completely through,
the next one in might breathe fresh air
(that next one might be you!)
Fucko Off!
Stratographers like to do it in beds.
I believe you mean stratigraphers.
I was going to post something, but all my favorites are already here, so I won’t. 
For a Good Lesbian Love-fest callinsert friend’s ph number here
Today is tomorrow’s yesterday
Look up at the footprints on the ceiling.
on ceiling Made ya look!
This Space for Rent
IDBB
Instructions on the Oval Office toilet seat, visible when it’s down:
“BM, W!”
“Why do they call it ‘taking’ a shit? I leave mine here - I sure don’t take any with me!”
Seen on a restroom wall on a military base, a remote restroom, quite a ways away from the main part of the base:
Flush twice, the chow hall is a long way from here!
LOL@Fritz*
That’s too funny.
IDBB