Muggy
British SlangDefinition
Brazenly disrespectful or out of order; behavior that treats someone like a mug (a fool) or makes them look foolish.
Examples
"Cracking on with your mate’s ex the day after they split is muggy."
"Bailing on the date without a word after she’d got ready was proper muggy."
"Posting our private messages in the group chat was muggy—you made me look like a mug."