Similar to how a gaydar is the ability to detect non-heterosexuality, the trapdar is the ability to detect a trap--that is, a male who can be easily mistaken for a female.
<A> That chick's pretty hot, I should ask her out.
<B> Don't. That "chick" is setting off my trapdar.
A sixth sense that only the wisest and most foolish people have; The awareness to events that lead to trickery and deception.
Commonly found in amphibians.
Mon Calamari: Admiral! We have enemy ships in sector 47!
Admiral Ackbar: (trapdar senses tingling) It's a trap!
(source: IMDB.com , "Star Wars: Episode VI - Return of the Jedi")