Creepy men who stare?

Just a curious question. I have been a stripper, and I have played roller derby. In each case, most of the spectators are men. They have fun, they whoop and holler and laugh. But then there is always that one guy - like in the picture I saw today in my most recent derby match - that is standing or sitting completely still with this creepy, unemotional expression. While everyone around him is cheering, hollering, and having a good time, this wierdo is leeering but not in a ual way...it's like he is angry and can't stand what he is looking at, but all the same keeps his focus on the women that are performing or playing. I want to know what the hell these creepy men are thinking. Any insight?