What a way to describe getting hitched. I got it from a Chris O'Donnell movie, "The Bachelor." Yea, that's how he proposed to Renee in the movie. Good thing she was in her right mind to refuse his proposal. But of course, they did end up together --- a happy ending.
It is crude for a guy to say such words in this particular setting. It definitely killed all the romance. Women dream of such moments, and will definitely be furious if their partner acts in such a manner. Uh, unless the girl is so smitten and blinded by the mere opportunity of being proposed to. Oh, joy. I can only wish her all the luck in the world that her married life will end in bliss.
But somehow if you really look at the phrase, "Shit or get off the pot", you will agree to what it actually means. If you don't mean to do the deed, don't bother sitting on it then. If you never really meant to marry the girl or even take her seriously, then don't get into any relationship with her in the first place. Some other guy will be decent enough to really "shit on it" so to speak. You can take your bad case of constipation somewhere else, I guess. Or better yet, here's some money for a diatab or go see a doctor. Or something worse, take a cold shower.