What are the biggest misconceptions about Mormons?

They are always nice. Not true at all. I've found Mormons to be extremely fake. When I was a Mormon, I was this way too. Every compliment and service act was always for another reason. In fact, the kindest people I've met are the ones who aren't Mormon.

rebecca_s

That you can easily talk them out of their religon. That if you show them solid evidence, they'll change their minds. Most of the time, mormons are so brainwashed that no matter how much evidence you have, they'll either 1) dismiss it as anti mormon lies, 2) attempt to refute it with very weak apologetics, or 3) start whining at you to "respect their religon."

amethystp

That the Temple ceremonies and buildings are a direct rip-off of Masonic lodges and rituals. Or that Mormons practiced (and still believe in) Polygamy. Just kidding! Those are true.
The biggest misconception is probably that the Mormons are a Christian church and not just a corporation with a tax exempt status.

That they are so giving and friendly to everyone, even if you aren't Mormon.

Most are friendly as long as there is hope that their actions will give you a positive impression of their church, and maybe some day lead to you becoming a member yourself.

If you reject Mormonism by leaving, the friendliness quickly disappears.

the-last-tapircorn

That they do not practice polygamy anymore. Men can be married (“sealed”) to multiple women but women cannot be sealed to more than one man. For example, the prophet is currently sealed to two women. Polygamy still exists as a doctrine. 

livsters

Mormons are not evil. They do what they do because they believe that they're doing the right thing.