Verb - to laugh so hard you pee your pants. This term is used in many SPAM email messages.
Lisa whizgiggled at the size of his penis and had to change her pants.
1 more definition
When you're taking a piss and something makes you laugh, and your dick starts shaking and you spray piss all over the place.
After John's joke in the men's room, Alex whizgiggled all over himself.