No such episode exists that matches that exact description.
The only episodes that come close are the one where he's jealous of Chris' endowment, that's And the Wiener Is & the other is the short fight they get in when Chris stop Peter from bullying, and that was Tan Aquatic of Steve Zissou
Chat with our AI personalities
They fight in Season 9|Episode 14 'Tiegs for Two' but the one you're referring to is Season 8|Episode 18 'Quagmire's Daddy'
Peter never really fights Chris but they do get into a fight in S05|E11The Tan Aquatic w/ Steve Zissou
Aired on November 27th 2011, Season Ten Episode Seven, the appropriately named, Amish Guy
it starts at episode 81 but im not really sure
episode 113
Their first fight is over episodes 435 and 436, their second fight is 449 and 450.
He first appears in episode 64 but his fight with Natsu doesn't really start till episode 65 then it's finished in episode 67.