ETA: Well, I goofed again. Silly me, expecting the Sundayverse to synch up now that we're in Retcon Country. It's a post-Halloween strip from 1980 that has John being a ranting hypocrite about the evils of excess candy consumption.
Panel 1: We start off with Mike mentally cataloging and wolfing down his haul from a busy night's trick or treating.
Panel 2: This attracts the disgusted attention of JSF. Typical. His wife is overburdened and he sits and smiles but let there be candy in his presence and he harrumphs "What a pile of junk."
Panel 3: He starts in with an angry tirade about how he, as a dentist, would like to make a formal complaint about all the candy consumed on Halloween. Fortunately for Mike, he's used to his dad's ranting so he's tuned him out.
Panel 4: He rants about how people eat enough crap without the candy-mania that arrives every so often; people should eat healthier. Coming from a guy who eats greaseburgers with extra bacon, that's a laugh. It's also hypocritical balderdash. While he's talking smack, Mike notices something rotten in the state of Candyland.
Panel 5: Y'see, he had two Whoopie bars and now they're gone.
Panel 6: He'd like very much to know who the rat that ate them is.
Panel 7: He quickly finds out: it's John "Do as I say, not as I hope you don't find out I do" Patterson, DDS (Dimwitted Dental Stupido).
Summary: John can eat all the candy he wants because his name is on the mortgage; he feeds and clothes Michael so all the candy belongs to him.