Thin privilege is being able to get a breast reduction whenever you want without having to worry about being denied for your weight.
Before any of the anti-SJ crowd starts rolling their eyes over this, let me point out something to you: first of all, the doctor who refused to perform a breast reduction on me has never even met me. My doctor tried to get a reference for me due to many problems resulting from having extremely large breasts, and she said no when my doctor told her that I was fat, even though she doesn’t know my height, weight, or BMI. Well, maybe your doctor gave them your physical measurements, you point out! No, they didn’t. Because they don’t know my height or weight, either.
Secondly, part of the reason why I wanted a breast reduction was because I am very limited in the types of exercises I can do because of them. Sometimes just sitting here I have to lean forward and pick up my bra off my chest so that I can breathe; needless to say, it’s almost impossible for me to exercise strenuously and be able to breathe at the same time. Another big reason why I wanted one was because I have trouble eating: if I wear a bra while I’m eating, I end up with indigestion because my bra is pressing so hard into my stomach, so I have to spend about half an hour after every meal holding up my breasts so that I can digest food properly. But all of that is less important, apparently, than the idea that I might somebody want to lose weight, and thus it would be pointless to do a reduction on me now, because what if I wanted to lose weight one day and they ended up being saggy?! The horror!
Thin privilege is being able to have a medical procedure that will help you right now instead of it being balanced against your hypothetical future physical appearance.