The part we don't know is how publicly he did it.
If it was very public like from a stage then it is not just harassment but defamation of a person by unprivileged oral communication made to a third party known as slander.
Also her profession could play a part in this type of case if her body fat is an issue for her job.
An action for slander may be brought without alleging and proving special damages if the statements in question have a plainly harmful character, as by imputing to the plaintiff criminal guilt, serious sexual misconduct, or conduct or a characteristic affecting his or her business or profession.
It's crazy but I've seen similar cases to this about calling people fat.
I'd say to apologize and offer something to her to make it better before it goes to court.
Just not a box of chocolates or something that will make her more fat. lol