To be all talk and no action
He bragged some much that when he didnt come out we knew he was an ocallaghan
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!!"
to bat for the other side
I was worried when my friend told me he was an ocallaghan
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.