…my foot!
Definition 1 of 1
Pro Tip 1/3Irony Usage
Used ironically, implies the opposite of what's being said is true. 
A reliable car, my foot! It broke down thrice this month.
Pro Tip 2/3Sarcasm Tone
Conveys a sarcastic tone showing you are unimpressed or skeptical. 
He's a genius, my foot! He can't even solve a basic math problem.
Pro Tip 3/3Informal Speech
Primarily used in casual conversation among friends or in informal settings. 
You cleaned your room? My foot! It's still a mess.