In many cases among men, the partner who penetrates another sexually is not regarded as homosexual, and
the receptive partner (who may or may not be consenting) is called a "woman", a "*****," a "punk," or a "prag," and is regarded as homosexual. In the United States in particular, rape in prisons is a major problem, and may be perpetrated by inmates who do not view themselves as bisexual or homosexual. One of the conceptions that tends to minimize prison rape and sexual coercion is that
the penetrating partner uses the act primarily to assert control or dominance, thus minimizing this activity as an expression of sexuality per se, an idea which is still repugnant to many, including perpetrators themselves. A man who has been raped, or who has been the receptive partner during intercourse, is often regarded as less masculine and hence a target for future rape and other violence.
http://en.wikipedia.org/wiki/Prison_sexuality