People should refrain from using (or alluding through sarcasm) stereotypes, especially on demographics that include people who read or participate here. It can be deemed offensive.
It would be the same if you had someone from India came on here and claimed that we were all hostile towards Indians (following the recent violence against them in Melbourne) - you would take offence at the generalisation.
I know a lot of nice Americans, as well as arrogant ones - but if a generalisation has the chance of being interpretted as a criticism of the entire demographic it is best to avoid using them in public situations here. Leave it for comedians and media criticts.