Thin privilege is this letter to Dear Prudence:

A: Let’s deal with the alcohol question first. If a 300-pound man has a couple of glasses of wine in the evening, I don’t see how that makes him an alcoholic unless he pours his libations into vases. You want to do something about your father’s weight, but as you’ve discovered, there’s really nothing anyone can do about someone’s else’s weight. Indeed, he may be significantly shortening his life. That would be sad, but if you make the time you two have together revolve around how big his coffin will be, then you’ll all be miserable. You can make a final stab at helping. Say you’d love to have him join you at Weight Watchers, or whatever, because you love him and want him to be around. If he won’t go then let him know that despite your worries, you’re going to stop cajoling and commenting on his choices.

Q. Dad’s Weight Problem: I am at a complete loss over how to help my father. He’s been overweight my entire life, and I’m reaching a point of feeling like I have to do something about it. I found out when I went home that he’s broken 300 pounds. My mother has tried countless ways to get him to start being healthy and losing weight, but it isn’t working. I’ve been overweight pretty much my entire life to some degree, though I never went as far as obese. I’m proud to say lost weight as soon as I went to college (I’m 20 now) and have successfully kept it down. But because of that, I understand what feelings my dad has if my mother or I try to comment on his weight. But it’s terrifying to see my dad like this. I fear for their marriage and for his life. I’m afraid he won’t be around to walk me down the aisle, or meet his grandchildren. He has also been a daily drinker my entire life—nothing more than a couple of glasses a wine a night, but obviously a problem. In the past few years, he’s tried on and off to stop, but my mother recently divulged she thinks he’s gone back to drinking, started hiding it from her, and even gone to hard liquor. The reprimand he gets from the occasional doctor’s visit only leaves an impact for a few weeks. Prudie, I am so lost and confused about how to help.

Notice the letter-writer didn’t mention a single unhealthy habit to support her opinion that her father is unhealthy except for his drinking, which, surprise! got worse from the stress of having his family constantly badger him about his “health”.

Notice also that Prudence seems to believe that fat = DEATH and doesn’t even seem to realize that the letter-writer hasn’t mentioned anything about her father’s unhealthy habits.

Thin privilege is not having beloved family members write to an advice columnist on how to better badger you about your “health” without once mentioning anything that actually makes you unhealthy (except for the drinking, which seems to be pushed aside here because apparently they believe that fat can kill you faster than heavy alcohol consumption).