Blindside Bitches Day is a day where you hit your bitch while you are out of their sight (for example, you hit them from behind). Blindside Bitches Day occurs on December 27th.
Dude 1: "Yo its Blindside Bitches Day lemme beat that bitch!"
Dude 2: "Ok"
Dude 3: "Bro you just pushed her of a cliff."
Dude 1: "Thats Blindside Bitches Day for you!"