You guys are too white for words. Gangbanging refers to being in a crime gang, its used particularily in respect to "black, urban" gangs such as the bloods or the crips and was popular during the 90s, when those gangs were huge.
you know, really i'd say three 6 mafia would be appropriate for either occasion...a group of people killing another group of people, OR 1 girl getting her shit destroyed by 12 different men at once...either way three 6 mafia just seems to fit the bill haha