Did Mormonism make a liar out of you?
I have seen people who became Mormons as decent, honest human beings become liars. It's not overnight, it takes time, but it does happen.
It starts out with milk before meat, but this is often used as an excuse to tell blatant lies to people.
For example, Mormons have been asked by other Mormons: "Do they dress up in costumes the LDS temple?"
The answer will usually be "no!" Which is, of course, a lie.