A phrase used automatically when you cannot come up with a comeback quick enough. "Your mom" means the same thing as "yo momma". Sometimes, if you are really lucky, using this phrase actually fits and makes a really good insult. You may have to say an actual sentence that plays on what the person just said and add "yo momma" to it. You can also use "ain't what yo momma said" to come back on a general rude insult someone says to you. This implies that you had sexual relations with the person's mother and she liked it. BEWARE. If you overuse "yo momma", it will not have its original sting.
This is a very good use of yo momma, though it might take a while to understand.
Annoying annoyance: Why is everyone acting so nerdy today? They musta got it from Patrick.
Patrick: They GOT IT from yo momma, you son of a slut!
This is an unnecessary, uncalled for yo momma.
Old grandmother: These cookies are fresh from the oven, sweetheart.
Grandson: Mmmm. Tastes like yo momma.