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1.
Having sex with two girls within a 3 day period.
Cody got his penis chopped off when Verna found out he had an Irish Threesome with her and Laura.
by Jp3 July 22, 2014
 
2.
Sleeping with two or more people within 12 minutes of each other. Derived from irish twins.
What did you do after that party? Wait, you nailed a chick from Suffolk and a Canadian 10 minutes later? Amazing! You had an Irish Threesome.
by the nomadic viking October 21, 2010