When I want to p.o. my in laws I do that....I can handle only three hours of eight people speaking (yelling?) in Spanish at the same time while I am trying to sip a bourbon before I say, "Is it a law that say's ya'll got to yell in MEXICAN when your'all talking?"
It's not ignorance or arrogance....It's called poking the bear....I get a kick out of it...
Similar to me referring to a good friend form Spain as "Mexican".
One time he was doing some yard work at his in-law's house in Florida when an old truck with a bedload of Mexicans with yard tools pulled up to the curb.
In Spanish "Hey - get in it's time to go!"
"What? Time to go?"
"Yeah, we're done, let's go home."
"I'M NOT MEXICAN! I LIVE HERE IN THIS HOUSE!"