"All that sugar is making you fat."
/I've been addicted to coffee since I was 15, and I drink it all the time. One time when I was out with my father, I put sugar in my coffee, and he looked at me and said, "All that sugar is making you fat."
He has made several offhanded comments about my weight in the past (although the doctor says I'm healthy for someone my height and age), but this is the comment that stuck with me.
I completely stopped drinking coffee for a while. Now I drink it straight up black because I have a fear of gaining weight.