Horribly. Happened back in college - we had a party for Halloween and we're all pretty wasted. The girl that lived across the hall came over with her friend that was visiting from out of town. The friend was pretty hot, but to make things better she brought a bottle of Absinthe. We were already drunk but holy shit did that escalate the night. New girl talked a lot with my then girlfriend (now wife!) and at some point pitched her on the idea of a threesome. My gf asked drunk me if I thought it was a good idea. I did my very best not to sound too excited. More drinks were had. The girls all went out to smoke. When they came back, it was on. We snuck off into my wife's bedroom, and things started off wonderfully. Lots of making out, rubbing, stripping out of already skimpy costumes. At this point I should mention that at no point in our hasty/drunken planning of this threesome were any ground rules discussed. We started having sex, and for the first five minutes things are fine. I'm fucking my gf and making out with hot new girl, everyone's having fun. A few minutes into this, new girl is really into it. She starts moaning "I need to get fucked." Drunk me happily switches gears, pulls out of my wife, climbs over on top of new girl and starts fucking her missionary style. This is when things abruptly change. Ten seconds into fucking new girl, my gf becomes jealous and starts crying/yelling at me to stop. In my head I hesitate because a) new girl is hot AF and I'm enjoying myself and b) this threesome was their idea in the first place! I do eventually come to my senses and stop, but by this point my wife's hysterical and runs out of the room. I pull on my pants and run after her. Eventually I convince her that everything's okay and that we just didn't think this threesome through as well as we should have. We go back to my apartment and pass out. By morning, new girl is thankfully gone. We haven't talked about it since, and Absinthe is strictly avoided.