mad stiffy - you're a walking joke, making faces like you're arguing with

you're a walking joke, making faces like you're arguing with your reflection while also being a total liar.

My teacher said I was a mad stiffy for cheating on the math test.

He called me a mad stiffy after I pretended to be a superhero in the school hallway.

My mom said I was a mad stiffy for eating the last slice of pizza and lying about it.