One Man Gangbang 

When you do something amazing that would normally take more than 4-5 people.

In Modern Warfare 2:

Guy 1: "Hey you just killed the entire enemy team in Ground War!"

Guy 2: "I know, I'm a one man gangbang!"

One Man Gangbang by DoctorGoodWood May 28, 2010

One Man Gangbang 

When one man starts a gangbang and no one taps him out because he's just that good.

Amanda: Hey look at Billy go

Sarah: Yea, he's a regular one man gangbang

Or

Amanda: hey Sarah how's your ass feeling today?

Sarah: Surprisingly not bad after having Billy, The One Man Gangbang. He's gentle!

One Man Gangbang by TeamNoSleep420 December 15, 2017

One Man Gang Bang 

When one man has anal, vaginal, and oral sex with one woman during one session, in any order. Also known as the trisexta.

Will: Want to go the bar tonight?
Bill: Not before 11, I am going to one man gang bang my girl in a bit.

One Man Gang Bang by DrSussy October 7, 2009