Forced bi is a practice in which the dominant partner forces the submissive to engage in sexual activities with an individual of the same sex. Within the BDSM community, the forced bi sex is a very common occurrence.
As an extreme BDSM scenario, forced bi sex is frequent in relationships where there is a female dominant and a male submissive. Usually, the males involved in these relationships are strictly straight. In this situation, the dominant humiliates her male partner by forcing him to have a sexual interaction with another man. In this sense, the male submissive is considered bisexual as he is having sex with people from both fenders. The forced bisexual activity can occur in any BDSM partnership too.
Regardless of the gender of both the dominant and the submissive partner, the whole point of the forced bi sex is to humiliate the so-called slaves. During the BDSM forced bi, the dominant can give orders as to what the submissive should wear or do. The disobedient submissives are almost always punished by their superiors with whips, paddles, electro sex toys, and more.
The forced bi as a regular BDSM play is so popular that there is a whole genre called forced bi porn, dedicated to this form of humiliation.