One study asked heterosexal men how comfortable and anxious they are around gay men. Based on these scores, they then divided these men into two groups: men that are homophobic, and men who are not. These men were then shown three, four minute videos.
One video depicted straight sex, one depicted lesbian sex and one depicted gay male sex. While this was happening, a device was attached to the male participant's penises. This device has been found to be triggered by sexual arousal, but not other types of arousal (such as nervousness, or fear - arousal often has a very different meaning in psychology than in popular usage).Hmm, this explains a lot.
When viewing lesbian sex and straight sex, both the homophobic and the non-homophobic men showed increased penis circumference. For gay male sex, however, only the homophobic men showed heightened penis arousal.
Heterosexual men with the most anti-gay attitudes, when asked, reported not being sexually aroused by gay male sex videos. But, their penises reported otherwise.
Homophobic men were the most sexually aroused by gay male sex acts.