Let's turn the table, for the sake of argument.

If I did and they felt offended (which, undoubtedly they would), they'd be absolutely right to feel offended.

But, then, they might just chuckle and chortle and call me, "You silly boy... but I can laugh at your joke," and let it all go at that. In which case, just because they're forgiving doesn't mean I was right to stereotype white-skinned Americans; greasy skin notwithstanding.

Whether Ostrom or Krugman would feel offended or just laugh at my "stereotyping" is their prerogative. Either way, I'd be wrong to generalize and they'd be right to be offended if they wish to.

I know a friend of my friend's who never got angry at anything, regardless of whatever name people hurled at him. People called him "Madey" all the time -- Kathmandu's admittedly popular pejorative epithet directed at Marwari community. He just laughed it away. Just because he laughed it away doesn't mean you can go around and commit double whammy -- using an epithet and insulting someone. Both is considered stereotyping. 

Stereotyping can be hurtful. Just because someone can laugh it away doesn't mean we all have to accept it. 

Pixie did not overreact. She was right to feel the way she did.