If you're referring to the episode 'He's Too Sexy For His Fat' (UK Season 3/US Season 2), it's because Stewie is gorging on fattening things such as chocolate cake and ice cream to rub in Chris' face the fact he's on a diet. Hope this helps! :/
Season: 9 Episode: 16 -- Big Bang Theory
Season 9 Episode 1
"He" ... exactly who is the "He" you speak of ?Brian, Stewie & Mort go into the past in Road to Germany.Peter & Brian go into the past in Meet the Quagmires.Stewie, Brian & Bertram go into the past in The Big Bang Theory.Stewie & Brian go into the past in Back to the Pilot.Stewie travels into the past (& future) in The Untold Story.
Robert "Big Buck" Maffei
Stewie sings in several episodes, "And the Weiner Is", "Ocean's Three and a Half", "Petergeist", "Emission Impossible", "Road to the North Pole", "Road to Rhode Island", a deleted scene from "Lois Kills Stewie", that's all I can think of off hand.
Season: 9 Episode: 16 -- Big Bang Theory
Mr Saturday Knight.
Season 7|Episode 3 Road to Germany.Season 9|Episode 16 Big Bang Theory.Season 10|Episode 5 Back to the Pilot.
Road To Germany (along with Mort)The Big-Bang TheoryBack To The Pilot
Business Guy
After "Sibling Rivalry" he simply ran off.He makes an appearance as the final boss in the Family Guy video game.And made his final appearance in the episode "Big Bang Theory" when he is killed.
Season 9 Episode 1
Season 9.
The Old Man and the Big C
Season 8|Episode 10 Big Man on Hippocampus
Season 8|Episode 10 Big Man on Hippocampus
The only song heard in Big Man on Hippocampus was Feels Like the First Time by Foreigner