I’ve never understood the prescriptivist opprobium for “ain’t.” The main knock against it seems to be that it is used as a contraction for several different word combinations (am/are/is/has/have + not), but the meaning is usually not ambiguous. It would seem to be the best available alternative for “am not;” other possibilities are themselves either ungrammatical or awkward.
Well then what is the past tense of shit? Would it be “shitted”, or “shat”, or perhaps something else?
Merriam Webster gives both “shit” and “shat.”
He shit an hour ago; He shat an hour ago; He has shit; he has shat.
For the verb form:
Yes, as are piss, snot, fart, fuck, and the like. I won’t buy a dictionary that would leave out those words.