Rugby dick occurs due to extreme cold or by ur dicks "6th sense" detecting possible injury to come while playing any outdoor sport in the cold. You have achieved "rugby dick" when your dick shrinks to the size of one of your testicles, or when you are able to piss on your own balls. This can also be used as an excuse for having a tiny cock in the locker room.
Fraser: "Woahh, watch where you're swingin that cashew nut!"
Allan: "It's cold out there gimme a break"
Fraser: "Aaah, got a bit of rugby dick going on I see, no worries, I won't judge you on your size"