When your buddies bring home a grenade and their vision might be cloudy due to inebriation, you can help them by grabbing a 'vuvuzela' and blowing loudly enough so that your buddy hears it and realizes that they are with a grenade.
"Wow Billy brought home a grenade, I have to help him out. (grabs vuvuzela and blows into it). Grenade Whistle!!!"
Billy: (hears vuvuzela) Oh Man Grenade!!!! Abort!!
Grenade Swarm (Verb) : To deliberately aim grenades at a single point from multiple players, so as to remove defenses from a long way away. Considered very bad manners, despite being a clever tactic.
It is often compared to camping and zerging, as both are considered weak strategies, while often being part of the game's design...
Base Defender: Haha, I am sniping you and you cannot... <BANG!> WTF?!?!? I'm dead! How'd I?!? You f*(!ing NOOBS, YOU GRENADE SWARMED ME!