someone who you do not want to anger... eg. a heavy hitter
don't screw with him, he's a mulhall.
by Bob Sacamano March 04, 2005
An "outsider". Someone your group of friends knows but doesn't like to include in anything because he/she isn't liked
Don't invite Johnny to the bar, he's such a Mulhall
by Ryan Mu November 05, 2008