A phrase so catastrophically devastating that any person who is willing to mutter these words in an argument will immediately win due to the enemy simultaneously combusting into flames
Phil:hi Dave did you sleep with my sister last night?
Dave:yo mama
Phil:*dies
Yo Mama is a term that can also be written as "Your Mom". Followed by these words are usually rude adjectives/jokes to describe one's mother. But, some may choose to refer to your mother as fine or a milf by using sexual references instead of hurtful words.
Your Friend: Yo Mama so hairy when she gave birth to you, you had RUG BURNS
You: Wow man that's kinda rude
Your Friend: Sorry dude, it's just a joke