Party Underwear
1.for girls: Party Underwear are a pair of cute or sexy panties worn when they know that there is a a chance they will hook up with someone at a party. 

2.for boys: Party Underwear is an adult style diaper worn under their boxers or briefs in precaution when they know there is a chance they might get too drunk at a party and soil themselves during the night. piss drunk 
1. "I'm wearing my party underwear 'cause Javier will be at Tad's tonight."

2. "Kevin better wear some party underwear tonight, because last week he shit his pants."