In men seeking men personals websites, pertaining to a male who does not identify with any gay or bi subculture as his own sexual orientation but still engages in sexual acts with other men and finds them erotic. It's a paradox of what he believes himself, what he thinks others perceive of him, and what he thinks his audience wants. He may or may not believe he is heterosexual depending on his psychosexual and psychosocial development.
This can be seen on craigslist personals and Manhunt among other websites.