If you are a guy, that means you would be having sex with someone who used to have a penis, and then surgically turned it into a vagina.
If a girl, you would be having sex with someone who surgically got a penis attached to them.
Would you have sex with this person for a one night stand?
How would you feel if you were in a long relationship with them beforehand, and then one day told you this. after you've already had sex? Would you be mad?
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Depends - I know a couple of people who've done exactly what you said. One went from Male to Female, the other did the opposite. But for me, it would depend on how attractive they were, how desperate I was and how much I liked the person.