(Strip Number 1430, Original Publication Date, 24 March 1989)
Panel 1: Since she doesn't quite realize that maybe Phil is actually laughing at the nut-bustingly stupid thing Mike said just now, Easily Outraged Killjoy Elly makes a smug remark about how he shouldn't hassle her about her (failed and misguided) activism because while she was marching for peace and justice, he was siphoning gas outta Jim's car and picking up chicks at the A & W.
Panel 2: While she was searching for inner truth (Honest, Mom, I'm just holding those marijuana cigarettes for a friend), he was getting stinko on Labatts and playing pool in some dude's basement.
Panel 3: She then says that while her 'generation' was trying to 'unite the world in peace and harmony', all his 'generation' wanted to do was have a good time. What this translates to in "Sane Person" is that Elly is always going to be angry because people are enjoying life when she's outraged by things and she uses Phil's being a happy-go-lucky goof as a mental image of "hateful slacker who should be made to apologize for smiling when she cannot."
Panel 4: Since Alan is a radioactive leper because he doesn't agree with Lynn's need to savage their mother's reputation, Phil is made into a pompous creep trivializing Elly's feelings by asking her if it's his fault she was born first.
Summary: This, I should think, is what drives Elly's need to stake a claim to a musical instrument that would never have been played. Happy-go-lucky Working Class Goofball Phil more or less rightly sees her as a self-righteous pain in the ass who mouthed slogans she didn't understand to make a big, showy display of herself while she sees him as an ungrateful wastrel who wanted to have a good time watching the world burn because she doesn't want to admit that she was the stick her parents beat him over the head with.