Thin privilege is holding (clothing, though this problem can extend to accessories like rings, bracelets, collars, chokers, necklaces etc) giveaways on your tumblr and not considering that some of your (often most loyal) followers might be above the tiny sizes you’re giving away or even way above them.
Thin privilege is obtaining things for your giveaways exclusively from stores that only carry tiny sizes.
Thin privilege is not asking the giveaway winner for their size and having an equally as cute prize in case they’re plus sized.
Thin privilege is using also including accessories in your giveaway as an excuse and as an option for plus size winners.
I know one could argue that those people are doing something nice by holding a giveaway and that one shouldn’t look a gift horse in the mouth and shouldn’t complain but the fact remains that fat people are excluded from that “something nice”… pretty much all the time. I think I have, in the crazy amount of time I’ve spent on tumblr in like the past two years, seen one single person who considered plus size people in their giveaway.