Calvin and Hobbes by Bill Watterson for September 28, 1990
Susie Derkins: I got a perfect score on my quiz. Calvin: You got a perfect score?? Susie Derkins: What did you get? If you missed any, you owe me 25 cents. Calvin: I ran out of time! I'd have had a perfect score too if I'd had a few more minutes! Susie Derkins: What did you get? Calvin: It's biological! Girls mature faster than boys! You just got a better grade because you're a girl! It's not fair! Susie Derkins: Pay up. Calvin: Maybe it's opposite day! Maybe all these X's mean my answers are correct! Maybe your "A" is really an "F"! That must be it! I win the bet!