The Big Bang Theory Season 1 Episode 4: "The Luminous Fish Effect"
Sheldon is fired from his job at Caltech when he insults his boss Dr. Eric Gablehauser. Unemployed, Sheldon quickly spirals into depressions which Leonard tries to end by bringing over Sheldon's mother.
Sheldon: I can't believe he fired me. Leonard: Well, you did call him a "glorified high school science teacher whose last successful experiment was lighting his own farts." Sheldon: In my defense, I prefaced that with, "with all due respect."