1. noun: General term describing someone of partial Irish decent who enjoys giving women (that don't actually want to date him) bruises. Typically the O'Fallon can convince any woman with low self-esteem that they should have sex with him, simply because they they are too afraid to say no. An O'Fallon usually has sex lasting no longer than 11 minutes. This is beneficial to the O'Fallon, since it never sees only one woman at a time. After sex, the O'Fallon's catch phrase is usually "This just isn't a good day for me."
Did you hear that O'Fallon is an abusive, misogynistic, dick head?