Peter ends up in a drinking contest with his real father, an Irish man who's the town drunk, in order to prove they're related.
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Family Guy Season 5 Episode 10 Quotes

Francis: (laying in hospital bed) Peter, come closer. There's something..I need to say to you.
Peter: I'm here dad, what is it?
Francis: Peter..you're a fat stinking drunk. (dies)

(dressed as a clown) Hey kids. I'm Pee Pants, the inebriated hobo clown. I'm an adorable tramp who wears found clothing and eats out of your garbage can.

Peter