"Family Gay"
He says a lot of things in that episode. Care to be more specific?
"Emission Impossible"
He doesn't. He says it to Chris in Season Three|Episode Five And The Wiener Is
It's season 4 episode 21. Titled "I Take Thee Quagmire."
Peter Kay was in the episode Love & Monsters.
Season 3, Episode 14: Peter Griffin, Husband, Father...Brother. Without ad breaks it's at about 13:41
I can't find that line in any episode, are you sure it was a Family Guy episode?
When he was repeating the 3rd grade
This scene occurs in Season 2, Episode 2 of Family Guy titled "Holy Crap." Brian hits Peter in the face with a newspaper and says "No" in response to Peter not heeding his advice.
Mia dumps Peter in the first episode of season 9
Season 2|Episode 8 I Am Peter, Hear Me Roar
Peter, Peter, Caviar Eater