The month when most men are single, because women find it repulsive for men to have pub like hair on his face.
If a woman was to make out for a long period of time with a man with a beard, it could result in beard burn.
Man- "wanna have sex"
Woman- "not until you shave that beard"
Woman- "If you're going to participate in no shave november, so will I. See how you like it"