ill explain it fully, but you might not like it. its a lot of stupid puns and wordplay going on because of course it is.
first off, in old samurai plays and movies and stuff theres a thing where they yell "chest!" or "chesuto!" and its a contraction of "chie o sutero" or "throw away your wits". like theyre running into battle so who cares about thinking, just go in.
so in wano they say "snatch!" or "sunacchi!" and its meant to be a contraction of "namae o sutero, chie o sutero" or "throw away your name and wits". in this case like, our individual names dont matter, we throw it away for wano, blah blah. this is why its supposed to be a big deal why momo isnt allowed to say it, because hes the kozuki heir and throwing away his name would throw away the only reason everyone else is fighting.
and the reason its "snatch" is because oda is a pervert and snatch is an old timey word for pussy, so. "chest", like boobs, and "snatch" like...