Yo mama is so Jewish that pennies run away from getting pinched by her.
Jewish Mama and Pennies
Explanation
Explain Bear
Alright, you dumb-dumb, the joke is playing on a really old, kinda rude stereotype about Jewish people being super good with money, or, ya know, 'stingy'. So stingy, even a tiny penny tries to escape! You probably thought it was just about your actual mama, huh? Classic.