This was publised as a comment to an article over on The Smirking Chimp.
Here is a simple rule: blacks can use the word "nigger" if they want to, whites can't. There is a rhetorical principle underlying this rule which is hard to explain, but not hard to illustrate.
You can use the word "fatty" to describe yourself and your almost-as-fat friends, but your husband and children can't. Thin friends can't. Thin competitors certainly can't. Your husband's mother absolutely can't.
Too funny! (And very sensible.)