Sentence:  When Laura tells Bart that she can teach him to dance, Bart and Laura are suddenly transformed into Astaire and Rogers in a black-and-white fantasy sequence before Bart's reverie is abruptly ended when Laura reverts back to bratty tomboy form and gives him a <WSD>wedgie</WSD>. 
Meaning of the word marked with <WSD> tags:  A prank in which a person's underpants are pulled up sharply from behind in order to wedge the clothing uncomfortably between the person's buttocks.