And I forgot another question that has been bugging me for some time. Anyone have any facts or WAGs about the expression “I’ve got to see a man about a horse” as a euphemism for going number 1?
Hopefully, any theories presented will remember to account for the fact that it’s almost always said by men.
I had always thought it was “to see a man about a dog”, it turns out both dogs and horses are used.
Try this reference
http://phrases.shu.ac.uk/bulletin_board/10/messages/441.html
It’s always been “see a man about a mule” here.
After thinking about it, maybe that should refer to #2.
If you listen to Car Talk, the phrase becomes “I gotta take a wicked haircut.”
Yeah, I second that. It’s a man about a mule. My favorite is “my back teeth are floating” because it clues you in immediately with a visual cue.
johncole, thanks for the reference. That lists alternate versions, but doesn’t really offer an explanation other than that it was a phrase used when you didn’t want to tell people where you were going. Is that really all there is to it?
“Excuse me, I gotta make a Jackson Pollock.”
Those words were spoken to me by a man that had just finished telling me about how he was only now getting over the stomach flu. I was in a bar at the time and everyone within earshot just died laughing. Ever since, my friends and I have always used the term “A Jackson Pollock” as a euphemism for a loose #2.
Later that night, the same guy came out of the john and the bartender yelled, “Another masterpiece?”
If I may make a slight hijack, what’s with the expression “…and the horse you rode in on”?
My favourite potty expression is, “I gotta shoot some hoops.” The last time, I got the response, “How’d the game go?” and I responded, “I tried to do a lay-up, but I fouled in the key.” Gotta love it.
See a man about a horse… Gotta pee like a racehorse…Coincidence I think not! 
It’s one step beyond F**K you, F.Y. and the horse you rode in on.
I’ve always liked “…and everyone who LOOKS like you.”
Yes, I think that is the whole story. In certain circumstances some people tend to become tongue-tied searching for a suitable way to say something they don’t want to be open about. Maybe they are embarrassed, maybe they don’t want to offend some third party’s delicate sensibilities, maybe it is just an accepted shorthand (e.g. number 1) that they learned in their childhood.
I would guess that it is used mostly by men because women don’t need to provide a reason to excuse themselves. (Nobody would dare ask “where are you going?”.)
I’ve always heard “See a dog about a man.”