A couple of years ago, when I was still in high school I used to be very close with a (chubby) girl in my class.
All of a sudden she started to act mean and giving me the cold shoulder, I'm fairly independent and I hate confrontation so I started going out with other people and that was the end of the story.
About a year later, I learned why she started acting bitchy around me, apparently we were having a snack during our free period and since it was summer she said she was trying to lose weight. I told her: Well, maybe you should not have a white bread nutella sandwich every day then.
I really meant it as an advice but it upset her so much that ceased to be my friend. When I heard it it, I couldn't believe someone could be so sensitive... Not a great loss for me though. Needless to say, she still fat.