Mirror, Mirror On The Wall ...

A red head, a brunette, and (of course) a blonde walk into a bar. The bartender tells them that in the bathroom there's a magical mirror that will give you something good if you tell it the truth but you lie you get sucked in.

The girls liked the idea so they all walked into the bathroom.

The brunette said "I think I'm the best looking person in this bar" and out popped out her prize.

Next the red-head and went up and said "I think I'm the smartest girl in this bar" it was the truth so a prize popped out of the mirror.

Next the blonde went "I think...." She was sucked into the mirror and never seen again.