I've always used my four-part definition of a cult (deifies man, humanizes God, ostracizes Scripture, and requires an extra-Biblical view of salvation.)

But today I learned of another one that rings true:

“You can always tell a cult from a religion. . .because a cult is just a set of rules that lets certain men get laid.”

(From the short story “Always” by Karen Joy Fowler)

For more information, see The Mormon Mirage 3rd Edition:  A Former Member Looks at the Mormon Church Today (Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.