A person who is a member of the Church of Jesus Christ of Latter Day Saints (Mormon), but doesn't follow their religion. They might get drunk and participate in pre-marital sex. This phrase traces its origins to high schools in Las Vegas. Antonym: molly mormon
1: Taylor got wasted at Steve's party last weekend.
2: I thought she was Mormon!
1: She's a jack mormon.
2: I thought she was Mormon!
1: She's a jack mormon.
by JFLV November 16, 2004
by Skibabyy18 July 01, 2015
Any class of hypocritical, self-righteous bastards that are members of the Church of Jesus Christ of Latter Day Saints and are prim and proper on Sunday morning and in front of other Mormons, but swear like sailors at work, secretly drink like a fish, cruise the net for kiddie porn on their work computers and are man-whores all over town.
"Always take at least two Mormons fishing with you or the damned Jack Mormon will drink all your beer"
by Demented Fish August 10, 2007