Bist Du dumm, oder??

So I have noticed that many people in Berlin will speak English (mostly with an attitude) when they hear one speak with an American-English accent.  In this case I have to say that I am less offended than I was last summer, but I am still faced with a conundrum—how exactly do I answer?

When I reply to an English answer with my slightly imperfect German, I get attitude, but when I answer back in English, that seems to irritate the other party as well! What is one supposed to do?

I have a tendency when I am seeking advice/help/service to want to speak with the other person in a respectful manner, because not only am I seeking help, but I normally don’t like to piss off the person making my food and drink.  However, here—I feel trapped sometimes, because at the same time, when someone yells at me for no good reason, I generally don’t like to give them my business. Kind of hard to do that when dealing with an irriated Kellner when trying to figure out the bill after I have eaten the food I wish to then pay for.

I realize that the standard of service in Deutschland is different (if  not non-existent) than what I am accustomed to as a North-American, but beyond that, I still have not figured out the way to handle the choice of languages: Englisch, Deutsch, oder Denglisch? Maybe a Mischung of alles? Wer weiß!!