The male version of the camel toe. When a man wears pants that are so small and wears them so high that his balls are visable through the pants. When pants are warn like this, his balls straddle the middle pants seam (just below the fly) thus dividing them causing the appearance of a buck knuckle. Similar to a camle toe.
Dude, since you gained weight you might want to consider getting some bigger pants. You're startin to sport some serious buck knuckle.