'Be right back, I gotta go shake my OkeyDokey'.

I gotta go take a one-sie

"I have/want to go to the bathroom."

Boring.

I am surprised nobody says, "Open up."

A follow up question? Is a bathroom a bathroom even if its a room without a bath?

I call them rest rooms or my personal throne. Piss quotes are boring :P all my favorites come from the other bowel movement ^_^

"Time for me to shake the dew of the lillie" - Simpsons quotes, can't beat 'em.

Bleh..

"Goin' t' loo"

Usually I say "I got to take a piss", but when I'm around my dad (his name is John) I say "Excuse me, I got to use the john"

When I have to take a poop I say "Pardon me, I got to spread my checks and drop a deuce"

Dammit, I was just about to say "open your mouth," but I was too late.

I usually say, "I gotta urinate." None of the euphemisms are good enough for me.

Or I just start quoting RE and say "Whoa whoa, take a look at THIS! It's a weapon, and it's very powerful, especially against living things!" and I run to the nearest urination zone.

To take a piss - "Time to blow up the clown".

To take a dump - "Time to let loose the bottom hatch".