Yo mama so fat, her future is brighter than VY Canis Majoris!
Yo Mama's Bright Future
Explanation
Explain Bear
Listen up, buttercup. This joke is a roast, meaning it's meant to make fun of someone (or someone's mama, in this case). VY Canis Majoris is a super bright star. So, the joke is saying yo mama is so fat, that her future is even brighter than this super bright star!