Responding Within the Frame LOSES
The most important single thing I can say is to not respond within the frame of the comment. Their comment puts you into the frame of:
- Still being a fatty despite losing weight, and
- Being someone who is easily taunted and responds to it by getting upset.
If you respond in any way within that same frame, which includes denying being a fatty, or ashamedly admitting it, or getting upset, or asking for them to stop, then you've already lost. You've already communicated low social status by any of these responses within their framing, and this is what they're looking for—to challenge your social status and see if you are high or low, and hopefully you'll come back as low status. They take pleasure in playing dominance games, and may not even realize this. That's because humans seem to be hardwired to always need to place people into a social dominance hierarchy.
Note: You might consider that losing weight actually threatens them because you might rise in social status and surpass them. When overweight it was easier to peg you as low. Returning from low status is a challenge to them, and they have to see if you can pass their tests to be admitted to higher status again.
Learn How to Respond Differently
All the above is mostly descriptive, but stay tuned, I have something prescriptive for you. Since I know that it is very hard to change how you react, and in particular very hard to "not get upset", instead of telling you a few things to try in text here, I have a much better resource for you: I promise that you will get better at handling these kind of challenging comments and social dominance games if you go watch the videos at The Charisma Matrix channel on YouTube. If you like, start with the video "2 Tricks - How to BEAT a BULLY everytime!"
A Caveat, and Personal Experience
I know the channel owner, Barron, seems a bit gimmicky. I know he wants ultimately to sell to you, eventually. But it can't hurt to watch a few free videos. What have you lost? I think this guy really does know some stuff—stuff that for me, personally, is changing everything. I finally feel like I understand some of the dynamics of my interactions with people that I never understood before. I'm finally getting why people are reacting negatively to me in some situations. It's all starting to make sense. And I feel such a greater sense of power and control. It's amazing.
Please let me know if you check out his videos and whether they help you.
There are other channels such as Charisma on Command that may be useful to you if you don't like that guy's style. I haven't checked them out, but will probably eventually get there.
More power to you!