A nutcase is someone a bit bonkers, unhinged, or just wildly chaotic in a way that makes you laugh, worry, or both. It literally riffs on nut meaning your head, like their brain’s doing freestyle jazz. Can be an insult, but it’s often said with grudging admiration for someone’s fearless, mad behaviour. Honestly, a pub staple.
"Jess turned up to the charity do dressed as a traffic cone and did a bungee jump anyway. Proper nutcase. Still, she raised two grand, so fair play to the daft legend"