Sorry @Gee54 I have only read all of your posts so far (and a few others on page 1), so I may well be repeating something someone else has brought up.
I am wondering how old your other children are and if one of them has recently been going through potty training for their poo's? Because if so I wondered if you were - quite rightly in my opinion - taking a laid back attitude to it, where whoever is present when it reaches the bullseye everyone gives a little cheer, and/or a well done? Or maybe the one going through being potty trained said they didn't like poos, or poos are horrible and smelly, and to encourage them your DD said something like "well, I like poos, yes they are smelly, but that makes them very funny!" If the 'worried about poos' child then laughed, and if which ever adult was present at the time then laughed as well, and if on top of that the adult agree that poos are (or at least can be) funny, then maybe it is possible that your DD liked that reaction - I know I would have - and so, maybe, even subconsciously, she has run with that hoping to make other people laugh!
Maybe your DD is a stand-up comedienne in the making, but has unfortunately already found her first harsh critics!!
For what it is worth (nothing I know, as I am a stranger) I think that your DD sounds delightful, and I love that she is a bit out of the ordinary; if anyone ever calls me normal I take it as a horrible insult! 🤣
Here are 2 💐💐 one for you and one for your gorgeous daughter - whatever the reason is for her little catchphrase xx