How not to chat up an American

Last week my friend Em and I were wandering around London looking for somewhere to quench our thirst. Walking past one particular pub, something caught our eye. A leathery man standing outside with a pint and a cigarette thought it was he. Actually it was the sign next to him declaring all drinks half-price today. “Go on in! You know you want to!” We did.
After we picked up our delightfully affordable drinks from the bar, we turned around to see that outside man had come in, and was headed our way. “I told ya. It’s a good place, in’t it?” Actually, the sign told us.
“Where you gals from, then?” Before we could answer, some emphatic instruction was added. “Please don’t say America!”
“OK, I won’t then.” I looked around for a table.
“I live in London,” added Em in a more friendly tone. She has much more patience for people than I do.
“Ah, so you ARE Americans!” As if he had beaten some sort of awful, embarrassing confession out of us. “Nah, that’s not all bad. I love America, actually. Well, San Francisco, anyway. The girls there are always all over me when I tell ‘em I ain’t gay.”
Sure they are, buddy. Sure they are.
“You’re not? Such a pity, since I only fuck gay guys.” I didn’t really say that. Instead I ushered Em over to a table in the corner. He got the hint and left us alone.
You might be surprised how many dudes in bars try to lead with the “You’re American? I hate Americans!” schtick. I’ve heard it a dozen times, and it still baffles me. I keep expecting them to follow it up with a discourse on how they despise pale skin and brown hair. Or talking to women.
What’s your favorite pick-up line? Does it involve an insult to the recipient’s country of origin? If so, please tell us in the comments how many times said line has successfully gotten you laid.