The concept where overweight and obese Tumblr users (usually white women, but not limited to race, gender, or sex) whine about how being fat is equal to the years of oppression similar to racism. More accurately, an ongoing game of sour grapes, wherein those too lazy to change themselves will instead blame society for the fact that they're missing out on all the best parts of life.
Many proponents of "thin privilege" also make claims that there are no adverse effects of being extremely overweight or obese.
400-lb woman: I can't fit into an airplane seat so I can't go to the All-You-Can-Eat Convention unless I buy two seats!
Friend: omg THIN PRIVILEGE!!!!
400-lber: Fat is a feminist issue! I can't help that I'm fat they're oppressing meeeee!! Oh hey pass the chips.
The state of receiving unearned social status, notoriety, workplace and academic merit, attention from prospective dating partners, media attention, and other perks from being perceived as 'thin.' Can also encompass greater access to healthcare, likelihood of attaining gainful employ, association with positive traits like being a good parent, person, or lover, accommodation in public and private transportation, and the ability to immigrate to New Zealand (check: there's a BMI limit) -- by virtue of being 'thin.'
#1: Thin privilege is not spending your entire life having people take one look at the size of your body and telling you that you can’t.
#2: Thin privilege is seeing a new doctor for non-weight-related issues, and not having to prepare, in advance, a long list of arguments and facts to present if your weight turns out to be the only thing they are willing to discuss.
#3: Thin privilege is not having your body type publicly humiliated in television shows like The Biggest Loser.