Well - I'm not as nice as most of you. LOL
I'd say something like, "Well, at least I won't look like a deflated balloon when I'm finished losing weight."
To the OP - it sounds like you are in an amazing period in your life. Standing taller and smiling are all parts of confidence, NOT cockiness or ego! Some people, just can't handle success for someone else, if they are happy. Keep doing what you're doing - pray and work for those that ARE inspired by you and those others, well, they'll have to find another way to feel better about themselves! (and it WON'T be by bashing you!)
Also - bottom line, you do not have to make excuses or plead guilt about surgery - it's a path that you chose. You don't owe anyone anything - no explanations, no backstory, nothing!
Good luck to you - you sound like a fabulous inspirational story!