Nine out of 10 overweight people experience fat-related jibes because of their excess pounds, researchers have said.
A survey found such name-calling is "endemic" among Britons, with 46% of those asked admitting having referred to or thought of an overweight person with a derogatory name.
But many of those hurling insults emerged as overweight or obese themselves when the survey of 1,000 adults calculated the body mass index of respondents.
The negative attitude was shared by people who had suffered name calling, with a third (33%) of obese or very obese respondents admitting to doing it themselves.
Weight-related bullying is most widespread among the young, with levels falling as age increases researchers found.
More than half of 16 to 24-year-olds surveyed (56%) admitted doing it, but just over a third (35%) of 55 to 64-year-olds said they had.
Almost a third of men had insulted someone for being overweight, in comparison to 11% of women.
Mandy Cassidy, of weight loss specialist LighterLife, which commissioned the survey, said: "It's sad that adults now find such behaviour acceptable. This type of prejudice isn't tolerated in any other walk of life - so we shouldn't allow it here."
"It is totally unacceptable and very hurtful. Far from discouraging obesity I found that it made matters worse and I now way about double what I should." - Rita Williams, Cardiff
"Although I would never condone these personal insults, it's often the way that some people are prompted to take action and that has to be a good thing. I deplore the nanny, overprotective state." - Yasmin Stevenson, Warwickshire