When confronted with a potential minor argument, both Dude and I do the "You're a--" repeating back the last word or phrase someone said.
While discussing why I buy certain types of foods for the cats, I came across the ultimate "You're a--" response, which I shall now use whenever someone tries to start small potato argument with me.
Imaginary Person: "Your mashed potatoes are bland and runny."
Me: "YOU'RE bland and runny."
IP: "You're being a child."
Me: "YOU'RE a nary tract infection."