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1.
A guy's best girl-friend, a.k.a. a girl he has no sexual desire for but is good friends with. The hetero version of fag hag.
"Wow, you tell Phillip everything!"
"I know! I'm a total het pet..."
by jane scearce February 15, 2008
 
2.
A gay man or lesbian woman who often hangs out with straight people.

Het is a shortened form of heterosexual. Pet
"Why are all of that dykes friend's straight?"
"She's a het pet ."
by MTAMTA August 04, 2009