Can you believe a brother would do this?

My brother and his friend both 15 were really annoying me so I locked them out of the house and my parents werent home, so they were really mad. i'm 13 btw. so they were banging on the door but I didnt care so I went upstairs to take a shower. 10min later his friend walks in on me and sees my naked! he left right away saying it was an accident, but I know he was just being a pervv. so after i got changed I was gonna get him back so I snuck and pulled down his shorts but he didnt have any undeerwear so i saw his ......ewww. but he had this weird looking bag like thing under his weiner, so i was making fun of him cuz it looked gross. what is that thing?