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1.
Yearly celebration of wedding day of two gay males.
This year, Brad and Josef will be celebrating their third manniversary, though the memories of their Fire Island wedding are as vivid as if it had happened yesterday.
by OhPuhLeez February 23, 2005
 
2.
The day to be remembered when to guys became good friends. Often celebrated with heavy drinking,throwing up, and passing out. The day itself is usually forgotten due the drunken haze of the day so it is celebrated around the same general time each year.
Joe1: You know Joe it was around Labor Day last year we hung out out at your place and got shit faced, Good Times

Joe2: Your right and its about that time of the year now. Happy Manniversary bro.

Joe1: Happy Manniversary
by DrinkinBuds September 06, 2009
 
3.
The anniversary of when bros became bros.
Denise: Wow, John, why are you so happy?
John: It's my bro and I's manniversary!
by Jakerzzzz October 02, 2011
 
4.
The anniversary of the day you lost your virginity.
Hey you wanna go out for some beers to celebrate my manniversary?
by Sean O'Connor December 20, 2006