1. When your scrotum adheris to your leg due to sweaty nuts. The sweaty nuts can result from tight emo jeans, driving (not just a truck) with out air conditioning, or a very hot day.
2. When your scrotum and penis stick together in an uncomfortable conglomeration of sweat and stickiness.
The cure for "Trucker Nuts" usually results from two stiff shakes of each leg.
"Dude its so hot in here you need a car with some A/C!"
"Hells yeah man I've got trucker nuts from hell!"