Use of the N word or saying that women are only good for bed and kitchen, and a person reveals their ignorance, overt prejudice, and will be rightfully chastised for such gross discrimination.
Call someone fat and lazy though, and for many this will be viewed as just calling it like it is, instead of what it really is, a judgmental, derogatory, discriminatory insult.
I think we need to deal as a society with obesity on several levels, one is preventing weight gain and losing weight, and the other, which I don't talk about much but perhaps should, is about how being overweight opens a person up to being discriminated against.
From overweight kids being bullied to obese coworkers being denied promotions or being the target of office gossip, I think we generally know this is wrong, but it isn't seen as being as wrong as racial slurs.
Discrimination against overweight people is as prevalent as racial discrimination
No more fat jokes - thestar.com
Bias, discrimination, and obesity. [Obes Res. 2001] - PubMed result
Obesity: attitudes of undergraduate student nurses... [J Clin Nurs. 2009] - PubMed result
Being overweight can prevent people from access to healthcare either from the individual dreading being weighed by the physician and any accompanying comments, or because some physicians are less inclined to do complete physical exams on obese patients.
Stigma and Discrimination in Weight Management and Obesity
Most of the population is overweight. Although overeating is being "normalized" by this trend there is still the irony of social stigmas being attached to being overweight.
When thinking about our health and fitness where being overweight is concerned, let's also be mindful of not being judgmental or discriminatory, as that has never helped anyone.