A lot of old Simpsons merchandise, both official and bootleg, had Bart in that blue shirt/purple shorts combo, which he has never worn on the TV series. The show eventually made fun of this phenomenon:
That was a weird flippin’ one-off line to turn into a T-shirt slogan, too. The school psychologist says Bart’s an underachiever and seems to be proud of it all the way back in the second episode. Bart doesn’t even say it; a character who appeared in a couple early episodes and then disappeared forever does.
That’s another one the show makes fun of later on. Bart’s rifling through his permanent record in Skinner’s files:
