If they are outright insulting you about it, tough luck. There are jerks in the world and they will be jerks regardless of your appearance. Grow some skin.
I'm guessing you've never experienced depression, anxiety attacks, or any other type of emotional disorder or abuse. I'm also guessing you have no idea how severe and debilitating these disorders are, and how they can greatly affect a person's lifestyle.
As an in-training corrections counselor, I've seen people from all walks of life who have many different stories to tell. Obesity is one of them. The "take responsibility for your own actions" idea only goes so far, and it doesn't work for everyone. Some people are not cognitively or emotionally able to take care of themselves. Others eat to comfort themselves because of their life situations. There are some who simply enjoy eating, but most of the time it's a symptom of a larger problem.
Human beings are social creatures, and the opinions and thoughts of others, no matter how much we'd like to deny it, affect us greatly and how we behave. When we insult, vilify and treat others differently or with malice, we distance and divide that group from regular society. In doing so, we only increase the behavior that caused society to reject them in the first place. Mental and emotional abuse should never be regarded as "tough luck". It's a very serious problem, and it doesn't just affect the obese.