Mug

Noun / UK Slang

Mug refers to someone who is foolish, naive, or easily deceived. It can also imply that someone is being taken advantage of or is unsavoury.

Example: “He’s such a mug for falling for that scam”
Means: “He’s so foolish for being deceived by that scam.”

Example: “Don’t be a mug and let them rip you off”
Means: “Don’t be foolish and allow them to take advantage of you.”