You sound like my kinda guy, cmyk! This is cracking me up.
Very rarely, when I’m feeling poetic, I’ll actually announce after the deed that, “my butt said something brown.”
And as someone who chose Dung Beetle as her handle here (as well as being apropos for this thread), I know that you’re my kinda girl! You’d have a blast at our Detroit/Ann Arbor Dopefests.
Sadly, I doubt I’ll ever make it. But if I do I’ll be sure to pull your finger. 
My Dad and I like to say… “Ive got to Rest”… derived from ‘going to the restroom’, which we thought was a funny term. What are you doing in the Restroom? Resting?
Another popular term used in my family, as of late, is to “Chagall” (the painter). We (my family) were in France at a Chagall museum last year, when my husband had to “rest”. A hilarious conversation ensued afterward and so for the rest of the trip we’d say… “I gotta Chagall”. This has followed us back home and we intend on putting a Chagall Painting in one of our bathrooms.
But to answer the original question… i’m with Poop. Poo is immauture! 
‘Poo’ sounds like ‘Pooh’, and causes an unpleasant association with a beloved character of my childhood.
Should I be moved to discuss my butt eruptions in a cutesy way, I go with ‘poop’.
I can’t imagine *any *situation in which I said Poo. *Maybe *Poop. But really, I doubt I would announce it at all, if I did, I would simply say I had to use the restroom.
I just lay an egg.
Shit. (or take a dump or a crap). Dogs and cats occasionally poo, but generally they also shit.
Do you “poo” or “poop”?
I take a dump, honeybunch. Or in the immortal words of the Greaseman, it’s time for a massive.
“Poo” is a term I associate with a constipated* 40-year-old woman.
*in more ways than one.
You sure? No one’s ever made it through all ten… Yes, I include the thumbs.
“Hey, pull my left ring-finger…”
“No! No more!!! After the left-index, I’m not sure my liver can take anymore.”
I knew I stopped back here for a reason.
The word is “poop.” I know, because I wrote the books on it.
I chose “poo is a noun, poop is a verb” but I also use poop as a noun. But poo is mostly a noun, “Dammit, I stepped in dog poo!”.
I also sometimes refer to farts as poots, it’s all in the poo family.
I agree with the wily one, but I prefer the all in one (verb, noun, adjective, expletive) shit.
The most important question (IMO) however, is who gave shit its unpopular name. After all, if it weren’t for the word shit, we wouldn’t need substitute words like “poo” or “poop”.
Couldn’t have been by the sound it makes, like “fart”, for instance.
Maybe long ago someone warned someone else, “Hey! Be careful! You’re about to step in some…shit, what do you call that stuff, anyway???”
Quasi
Yeah, I’m with you. I might tell people that I’m going to the bathroom or restroom. I never feel the need to explain exactly what I’ll be doing in there.
But if I did, I think that takin’ the Browns to the Super Bowl would be my announcement of choice.
I love the term “doot,” and use it all the time to refer to my cats’ output. “Okay, gotta go scoop the cat doots now.”
Both the spouse and I picked it up from Dave Barry years ago. I think the first time I encountered it, he was talking about their movers, who “wrapped each individual cat doot.” For some reason I found that devastatingly funny at the time.
The word “doot” still makes me giggle.
As for what I do, I “go to the loo.” I don’t really feel I need to get any more specific about it than that. Though at home I"ll announce “I gotta pee,” so careful listeners can make their own deductions if I say I’m going to the loo instead.
By process of elimination?
Yes! Only in the one I remember, he was talking about getting hit in the head by a flying caterpillar doot. 
The diminutive version is poo-poo. Poo is a stuffed bear who can’t spell.