The point at which a woman's craziness outweighs her level of beauty.
For a woman to be considered "below the Mendoza Line," she must be sufficiently crazy that it doesn't matter how beautiful she is; you would still not sleep with her.
Based on the baseball term of the same name, referring to the point at which a player's poor batting average cannot be justified despite his defensive abilities.
George- "Dude, Suzy's all over you tonight. Why are you ignoring her?"
Brett- "Trust me man, she's way below the Mendoza Line. Her last boyfriend had to change his social security number."
The absolute minimum effort or accomplishment required to be considered sufficient. (Named after Minnie Mendoza or Mario Mendoza, depending on whom you ask -- two major-league baseball players with lifetime averages around .200.)
"I was going to buy that oldSuburban, then I find out it gets 10 mpg, and I'm like, 'No, that's below the Mendoza Line.'"