Yo momma so fat, they made a size for her. Small, medium, large, extra large, and Yo Momma.
Yo momma so fat, she had a revolution. Now she’s the People’s Republic of Yo Momma.
Yo momma is so fat when she turns around she causes frame dragging of space time.
Yo momma is so fat she checks her weight at a highway weigh station.
Yo momma is so fat she has her own zip code.
Yo mama is so fat she has her own area code.
Yo momma so fat Neil Degrasse Tyson upgraded her to a planet.
Hah! By far the best one in this thread. 
What’s a twelvsie? (Yes, I googled it, but I got nowhere.)
Thank you! I either made it up on the spot, or remembered it from a reaaaallly long time ago. Not sure which 
Boomerang belt gets my vote so far.
Yo Daddy so fat my car cried when he got in.
Yo Daddy so fat when the rip tide caught him the lifeguard called a tug boat.
Yo Daddy so fat, Peapod sent his order in an 18-wheeler.
Yo Daddy so fat, he showers at the car wash.
Your momma’s so fat, she’s being stalked by Captain Ahab.
Hmm, racist and classist - can only be used in reference to white women with a semi literate child. 
Yo momma is soooo fat…
…it takes her 10 sheets to wipe her butt - California King.
…last time she sat on the sofa it took 3 men 2 days to dig it back out of the folds.
…when she laughs, surfers fight to ride the waves.
I take great offence …
… it requires a fully literate child.
Nah, the event horizon belt.
I’m surprised this board of nerds isn’t celebrating “Thanos had to snap twice”, which I came into the thread to post but found it already here.
Your momma’s so fat she can’t be executed by the moon door.
Your momma’s so fat she’s married to Roose Bolton.
Your momma’s so fat even the strongest chains and all the wights in the world can’t pull her out of the lake.
Your Momma’s so fat, she went to the beach and the lifeguard asked her to move so the tide could come in
This will date me, but…
Your momma’s so fat that after sex, she smokes a ham.