You can say "Stupid Americans..." and nobody would think anything of it, but as soon as you say "Stupid Africans..." or something of the sort, all hell would break loose, amirite?

Stupid Asians...wait, am i even allowed to say that?

Because Americans are stereotyped as being stupid, and if you called someone from Africa stupid, they'd feed you to their pet lion.

Americans always get pissy when I say Americans are stupid.