Plot hole: It is shown that Marge first met Luann van Houton when she was ten. But in "Homer Defined", Marge said that she first met Luann in an emergency room when Bart and Milhouse drank paint.
Plot hole: A little ways into the episode, when Milhouse kisses Homer, he says that was the first kiss in his whole life. However, we see him kissing Samantha Stanky in the episode "Bart's Friend Falls in Love," in Season Three.