Interrupting Sizism

Just now I watched part of a Friends episode--the one where they play out what they'd be like if certain changes in their lives hadn't occurred. One of those "what if"s is what if Monica hadn't lost weight? And, wouldn't you know...there are all sorts of subtle and not-so-subtle jabs at the "fat" Monica. I couldn't watch very much of this...it was almost-physically painful.

Making fun of people because they are fat is not cool, period.

What I want to know is: Why is it still "acceptable" in today's society to do so? How is it that we've come to the place where we've realized that it's not OK to make fun of people's gender, ethnicity, skin color, sexual preference, etc.; but we still think it's OK to make "fat" people the brunt of jokes?

More to the point, what can we do about it? The Council on Size and Weight Discrimination  advises,

Interrupt sizism. Notice when something you see or hear is discriminatory against larger-than-average people. Don't laugh at "fat jokes". Interrupt sizism or weight discrimination when it is possible by pointing it out and expressing your opinion that it is wrong.

In other words: Speak up. It's too late for that Friends episode, but the next time I see or hear fat jokes, I'm going to "interrupt" it.

Who's with me?