The opposite of gaydar. An ablilty to sense heterosexuality in another being. Useful when your newly uncloseted friend decides that every attractive male with a sense of style is gay, and tries to trump your totally logical arguments to the contrary by proclaiming to have gaydar.
gay dude: "Your buddy Steve is gay."
not gay dude: "no he isn't"
gay dude: "believe me I have gaydar, he's gay as Christmas"
not gay due: "Well I have hetdar, and he's about as gay as Wilt Chamberlin"
gay dude: "oh..."