I find that replying with a few words of Samoan or Italian REALLY ticks them off!
They have no problem at all with carrying on extended conversations in spanish, while nodding and smirking in your direction, and laughing.
Turn the tables on them with a third language (or even a good made up one) and they HATE it, they will DEMAND that you translate what you said.
I used to do this at the last large company I worked for, before long the illegals there stopped playing their rude game of speaking spanish in my presence.
Something I am surprised no one brings up, if employees do not understand English and there is an emergency they will suffer more casualties than the English speakers.
In fact it would not be hard to prove this, I clearly recall several examples, the most recent being a paint recycling plant and an explosives factory.
There were non-English speaker fatalities at both.
igPay atinLay