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adj. The act of still having your virginity in college while being surrounded by drunken pussy 24/7. Drinking excessively almost everyday for no apparent reason while also going on explicitly long rants about nothing that have no relevance to the pertaining situation. Not showering for days at a time is also a trait of O'Callaghan. In summary, the act of completely embarrassing the Irish race one drunken night at a time.
Guy 1: "Hey man is he a pedophile?"
Guy 2: "No, he is just O'Callaghan!!"
by Stone, Keith September 15, 2010

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To be all talk and no action
He bragged some much that when he didnt come out we knew he was an ocallaghan
by Hardcore September 08, 2003

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to bat for the other side
I was worried when my friend told me he was an ocallaghan
by Sean September 03, 2003

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Adjective: (irish) Used to decribe a man (or young boy) who bails on his mates early in the evening.
... so we were up for a hyooge one and had hoovered a load of coke, on our way to this bar right, when he says "I'm going for a quick walk around the block" ... what complete a cunt, how totally ocallaghan.
by ASDADSA 187 September 05, 2003

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