There's apparently a five-second test you can perform on yourself to see if you lie like a rug. It was developed by Richard Wiseman, who wrote 59 Seconds: Change Your Life in Under a Minute.
Basically, what you do is draw an imaginary capital "Q" on your forehead, then take note of which side of your forehead the tail is facing.
If the tail is on the right, you're not a good liar, and if it's on the left, you're great at lying. When you're drawing the letter "Q" with the tail on the left, you're drawing the "Q" in a way that's legible to an audience. This means that you're aware of how people perceive you, which translates to being an extrovert, enjoying attention, and major lying skills.
This would be a fun test to try on friends to get some quick insight on their personality. Here's a video that explains the whole test: