The teeth movie really freaked me out, but why?

OK so I'm not really a squeamish person, I watched all the Saw movies, Texas Chainsaw massacre, etc. without so much as a second thought. But after I watched a movie called teeth ( link ) I felt really creeped out, obviously most guys might cringe a bit but I mean I really have been obsessed with it. It also affected me to see that the girls I was with thought it was hilarious...really? I don't know sexual mutilation really bothers me, I really hate seeing rape scenes in movies 2. Girls, is the idea of a guy being sexually mutilated really funny? and why am I freaked out particularly by this kinda stuff? When all other blood and gore has no effect on me at all.
The teeth movie really freaked me out, but why?
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