Those who try to charm you get an unpleasant surprise.
Prerequisite: Exposure to charm or dominate spell.
Benefit: When you succeed on a save against a charm or compulsion effect, the character trying to charm or compel you believes that you failed your save. You can play along voluntarily if you wish to. If the charm or compulsion involves telepathic commands, you continue to receive them, although you aren't obligated to follow them.
Source: Unearthed Arcana