when you sit on your nut sack and one of your testicles goes up your ass crack and you have to pull it out. Thats when you loose your marbles.
sean: mate why are you wriggling around like the purple gay wiggle?
Guy: man ive lost my marbles, i might have to hang a shit to pop it back out again. quick go get the chilli.
sean: lost your marbles? man you only ever hear about this kind of shit on the discovery channel.