I think that comment alone is probably a reason. I like the idea of you asking this so you can improve, but calling people "quivering little pussies" will only make them even more scared of you. The word choice of name-calling i guess is something that counts towards why they might talk behind your back, because if they told you in person you'd only call them unkind words. I don't really interact with you that much so I don't have a lot of problems, but thats just a major problem the majority of people have with you.

If you really want them to open up to you so you can work the problems out, maybe being pissed isn't really the right state in mind you should be when you address this to them. They'll only close up.

It's okay to feel pissed they are doing that. I'd be mad if I heard people were talking behind my back. Although since you are trying to change and again, be open about the problems, you'll have to try and channel your anger because calling people names and throwing negativity at people that already have problems with you wont solve them. Not saying you are that bad, but I know you can tone it down.