1.) testicles. used to nut-out jism.
-British slang adjective
2.) nutter in singular form refers to a/an jack-off or asshole person.
Man, did you hear that dudes woman swamp-stomped his round n' lows and threw him out the house? I hear he just took it like a little bitch. Fuckin' nutter(jackoff)!
He thought I parked the car shitty so the fuckin' nutter (asshole) keyed my shit up.
Also probably the most common mistake made by outsiders when trying to reproduce a British accent. For the record, it's either "he's a nutter" or "he's nuts". Saying "he's nutters" is a good way to make British people dislike you.
Bad: "Are you completely nutters?"