How do I stop being such an effing perv?

I constantly catch myself checking guys out, especially their asses (for example went for a swim nearby, man in a wetsuit comes and it hugged his ass perfectly and yeah I stared for a while). I look at guys forearms, I look at guys asses, I look at their everything, constantly checking them all out. I do this CONSTANTLY to many guys though (like 40% of passerby I will check one of the above...) and I have a VERY low sex drive, so I'm confused! It bothers me, why do I subconsciously do this if I'm not even desperate for a good fuck? How can I control it before I get punched for staring or some stupid shit like this? Is it normal to be doing this so often?... if it is, guys who wear tight fitting pants... please keep doing it. Never stop. It's perfect.