The origin of this slang word is the TV Ad for Dime Bars (now Daim, made by Kraft Foods), a chocolate covered crunchy caramel candy bar, which aired back in 1995.
The Ad featured the British comedian Harry Enfield playing a slobbering retard in a supermarket, filling a shopping trolley FULL of dime bars... he's approached by a well spoken interviewer (Also Harry Enfield), who asks him 'Do you remember your first Dime?'... anyway, the ad finished with the retard exclaiming to his wife:
"That bloke's a nutter... OI, NUTTER!"
Google the phrase 'dime - that blokes a nutter' and you'll be sure to find many videos of this wonderful ad
Many of us will also remember the Armadillos from the second ad they did!
Oi, Dime Bar!
Lookout! Dime Bar alert! (nutter approaching)