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1.
When on any of the Halo games on Xbox Live, or a multiplayer Campaign, that you rapidly squat up and down, giving the impression that you are humping someone else. Used mainly on Xbox Live to show ownage after killing someone.
Xbox Live player one: nah nah nah nah nahhh nahhhh! you can't kill me!
Xbox Live player two: *kills with sword* HAHA N00B! *has halo sex*
Xbox Live player one: ---
by squirrelyy. August 10, 2007
 
2.
when someone is playing halo and starts jacking off to it
chase says:so mike do u like girls yet?
mike says: na , im into the halo sex thing
chase says: whats that?
mike says: when you jack off to halo
Brandon says: oh yeah me and mike did that
by Grizzlies 16 April 29, 2006
 
3.
Having sex while playing halo and getting a certain number of kills.
Yeah, my wife and I had halo sex last night.
I had more than one head shot if you know what I mean.
by Biznasco January 27, 2008
 
4.
bribing your girlfriend (or gay guy friend) to dress up like master chief before you give them anal sex. it works in other places as well but the asshole is best because it is universally available on all candidates. less common but equally effective costumes include: grunts, elites, warthogs (vehicle or animal), cortana (try this one with your guy friend :P), and flood (those things suck like you can't believe!!). playing halo at the same time adds to the experience (try that on legendary!!).
so lets say you are bisexual. you have your girlfriend and guy friend over for the night and you can't decide whether to play halo or do something strange involving sex. DO BOTH OF THEM YOU FUCKTARD!! have her dress as master chief, have him as cortana (or a warthog :P) and "cock and fire" in both halo and real life. you'll have so much fun, you will talk about your halo sex experience on the forums (and live) for months!!
by Bliz Nix May 09, 2008