It is the annual anniversary when two, or more, people banged.
It is a highly celebrated holiday by men that rejoice upon the fact that banged a member of the opposite sex, aka a 'Hoe.' Men usually do not purchase a gift for this anniversary but may use it as an opportunity to again bang the woman they have already banged a year previously.
It is usually a period of mourning for women that were inebriated and made a poor decision to bang a certain gentleman. Many times a 'Bangiversary' invokes women to go to the bar or club to get wasted which again creates the conditions of banging a dood they will regret a year from now when the 'Bangiversary' comes. This results in creating a perpetual cycle of sorrow and misery. The few exceptions to this is if said gentleman is a basketball player or rapper and the female is now rich from the baby created. She celebrates her "Bangiversaries" lavishly.
The greatest reminder of a "Bangiversary" is usually an unwanted child and/or genital warts.
Yo, I think I banged that bitch a year ago. Time to celebrate da bangiversary and drop a load in dat ass!
Man my genital warts acting up again and shit. I should never have fucked that dirty skank motherfuckin' hoe a year ago. Fuck it a nigga gotta' empty deez nuts time for a "Bangiversary."
Man fuck this child support. Bitch got pregnant on purpose. Fuck dis baniversary. I'm going to go fuck another bitch but this time that hoe is swallowing dis nut!
OMFG I can not believe I banged that ugly son of a bitch and he had a small dick! I need a drink and a valium to forget this bangiversary.
Yeah I fucked that dood. Weak ass mother fucker couldn't even last 2 minutes before he busted his nut. All I got for my bangiversary was this bastard of a child. Fuck it I'm going to da club!
Thank Jesus for this bangiversary! This mother fucker is rich and I'm getting all that money.