Yo momma's so ugly she turned Medusa to stone.
Yo momma's so stupid her INT score penalty has two digits.
Yo momma's so fat, they had to make up a new size category for her (Gigamomma'normous)
Yo momma's so fat, they use a grapefruit for her miniature.
Yo momma's so fat, she can't see her feats.
Yo momma's so fat, her speed is listed as "HELL NO"
Yo momma's so fat, her favorite sushi is Aboleth Rolls.
Yo momma's so fat, her Character Class is Buffet Clearer.
Yo momma's so fat she won't fit in a bag of holding.
Yo momma's teeth so yellow, when she smile people think she's really a Gold Dragon
Yo momma's so fat her mini is a tub of Crisco.
Yo momma's so cheap, she asked for a discount on Bucknard's Everfull Purse.
Yo momma's smells so nasty, she makes otyughs retch.
Yo momma's so old, Gary interviewed her to determine the right Hit Dice for every dinosaur.
Yo momma's so ugly, Cthulhu is the one rolling sanity when they meet.
Yo momma's so stupid, Mind Flayers won't eat her brains.
Yo momma missed with a Wand of Magic Missiles.
Yo momma's so stupid she dried up a Mind Flayer when it tried to devour her brain.
Yo momma's breath so bad, she an honorary green dragon.
Yo momma's so dumb, you bought her some Chainmail and she sent it to 10 of her closest friends within 3 days.
That's all I got.
Now tell me someone else here plays DnD, so these weren't a waste of time.
Edit: Credit to this thread:
http://community.gencon.com/forums/t/21289.aspx?PageIndex=1. This is where I got all these jokes.