Wiktionary
vb. (context vulgar idiomatic imperative English) Make a decision, especially after a period of delay; either commit to action now or forgo the opportunity.
Wikipedia
"Shit or get off the pot" is a common English language colloquial expression, used to imply a person should follow up their stated intentions with action. It is also used to urge someone to complete a task with a greater degree of efficiency or timeliness than is observed at the time the expression is used. Implicit in the expression is that the person, by failing to act, is preventing others from acting.
Usage examples of "shit or get off the pot".
We're telling the crumbs of this world to shit or get off the pot!
He knew that down below they knew they had to shit or get off the pot a lot sooner.
After almost thirty years of marriage, that sound still makes me want to turn on her and yell at her to stop it, to shit or get off the pot, either say what she means or keep quiet.