This is something that is really bothering me. I try to accept everyone even if i dont like some things about them....but I really get grossed out by fat people.

You probably assume they're fat because they're greedy, and maybe it is the impression of greediness that disgusts you?

If you were around someone who was abnormally greedy for something else, for example buying expensive clothes, and this was somehow visible, e.g.: the extortionate amount of money the spend on clothes meant they could not afford basic things like medicine and soap, which was resulting in an adverse effect on their health, you'd probably feel a bit disgusted too, at their lack of self control and inability to see what is more important?
Bad example sorry, but it's all I can think of right now.

It could be an inbuilt subconscious 'self-protection' mechanism- if you thought it was acceptable to be fat, you might get fat too, lowering your life expectancy.

I read an article once claiming that obesity could be 'catching'- like there was a virus that changed your DNA and it resulted in people being more susceptible to getting fat- so again maybe it is an inbuilt mechanism to get you to stay away from the fat people the same way as any other contagious disease.

I'm not sure how much evidence there was backing up this claim BTW, I don't think the majority of obese people have 'caught' it off someone else through a virus.. I think somewhere it said 30% of overweight people had antigens to this virus (so they had had contact with it)..