Top definition
a saying used to stop people who should not be hooking up from doing so

in general any situation where something is prohibited, should be followed with people saying "nun's bar"

can be accompanied with a jumping forward and crossing arms in front of each other, as an umpire would do at a baseball game
"omg! don't hook up with him! nun's bar!!!"
by the whirlwind November 12, 2006
Happy St. Patties Day!