Top Definition
An O'Neiller is when someone is on the down and out in some shape or form, and decides to grow a beard and lets their Appearence Dishevel. It often occurs in men between the ages of 27-40, It is not to be Mistaken with mid life crisis. O'Neillers are bred from hatred and often the lack of Sexual Intercourse.

Folklore tells us that the Famous O'Neill was Roland Turlogh O'Neill, a feared Celtic warrior from Carlow town who was also said to have been a fantastic painter/decorator and a very Agressive Bearded lover.
After Patsy left him, Joe went on a terrible O'Neiller.

"God whatever you do, dont poke fun at seans beard, I hear he is in the middle of a terrible O'Neiller and is liable to do anything!
by SKetchgarda December 17, 2009

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