"Nobody take shit from nobody." should be corrected to the common phrase "Nobody takes shit from nobody" However, a lot of people say this phrase, not knowing it does not make sense. It uses two 'negatives': "nobody". This means that no one can take grief from no one. This is impossible, as nobody can be giving you this grief. As Spangola said, the correct way of saying it is "Nobody takes shit from anybody." The meaning of this phrase is that it is saying "Not a single person takes shit [grief, hassle, abuse] from anyone else.". They should not be abused. You should also note "shit" is a curse word in the English language. Some people find it offensive to say, so be careful using it.

You're right, it's not about excrement. The word "shit" in this context means a number of things like grief/hassle/abuse/bad manners etc. I think you meant to say "Nobody take shit from anybody," because "nobody take shit from nobody" doesn't make sense. It's "take" because it's in the imperative form, it's an order.