When they first realized that Big Guy's AI would not work.
Mechanic: How many fingers am I holding up?
Big Guy: Thursday.
Pretty much anything Big Guy says in the second half of the episode "The Inside Out" after his repaired AI starts malfunctioning.
"As the jackal is drawn to moonrise, so draw I ever closer to my waiting foes."
"The only offense is the way that mailbox was laughing at me."
"I just want to talk, too, pal. I wanna talk about the size of the roots on these tubers [waving a streetlight around]...and I wanna talk about the cut of your jib!"
"Time to get hoppity!" (takes off) "I can fly! ... Hey, backscratcher!"
"Sshh, quiet son. You're scaring the fish!" (Said, while inadvertently menacing a trapped and cowering family, to Rusty when he shows up to talk the Big Guy down.)
When Big Guy gets misdirected and crashes a wedding.
Priest: If anyone should wish to offer reason why this bride and groom should not be joined in holy matrimony, let them speak now or forever hold their peace. Big Guy (breaking through wall of country club): Anyone for pie? Piping hot! [looks around] Best wishes, citizens.
Later he interrupts a bar mitzvah in a similar manner.
Just about any scene with the green, yellow, and red robot malfunctioning and clobbering each other.