No, it is not ethical at all. Humiliating someone based on any physical characteristic is a form of body - shaming. Everyone should be respected regardless of their body type, and spreading such stories can cause great harm to a person's self - esteem and mental health.
If you come across such stories, don't share them and encourage others not to as well. Also, promote positive body image campaigns to counter such negative ideas.
I think it's not as common as some other forms of humiliation, but it does happen. For example, in some sports teams, if a player has an accident on the field and has to be put in a diaper - like protection for the rest of the game, some teammates might make unkind remarks. However, society is becoming more aware of the harm of such humiliation, so hopefully it will become less common in the future.