why can't some people mind their own business

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I am willing to admit that I am super grouchy today from lack of sleep but one of my coworkers just really ticked me off and I have to get it out. She had a weightloss surgery last year and has done a great job losing weight. I really am proud of her.but she really ticks me off because now she is the expert on weightloss. I was having a protein shake for breakfast this morning and she began critique what I had put in it then asked me if I was counting all the calories of the ingredients. Then she informed me that I was still eating too many calories and I should drop down to 1200 if I want to lose weight. I just hate it when people start judging me cause it makes me feel like I am not going to be able to reach my goal so why even try. I WILL NOT BE DEFEATED THIS TIME!!! Sorry I just had to vent.