When something is based-pilled, it is a joke used by combining the slang word based, and the “red pilled” slang first used in right wing subreddits.
Person 1: Hey, did you get pizza with sausage or pepperoni?
Person 2: I got pepperoni on half, and sausage on the other as Person 3 likes sausage.
Person 3: based-pilled