Mug

British slang

To describe a person as a "mug", they are stupid or daft

To be a "mug", means you are a fool, daft or have just said something stupidly funny.

To "mug" someone off, to win an argument or prove someone wrong which makes them look foolish or silly. (you can also mug yourself off by doing something stupid)

"what a mug."

"you're such a mug"

"jenny just mugged you off"
"you just mugged yourself off"