A belly wart is when you pull one of your testicles up above your pants. -while wearing you pants normally. Your nut, whichever one you chose to pull up, looks like a huge wart right above your belt.
Dude- "Yo bitch, did I ever show you my belly wart?"
Bitch- "Belly wart? No you haven't."
Dude- "Check it, I have had it since I was born."
Bitch- "Ewww, WTF Dude!"
Dude- "Aha, dumb bitch."