Worrals,
We're only human, the American bloke was probably just having a bad day and you were the unfortunate soul he took it out on. Not very professional though, it must be said.
Just try imagining the atco on the ground isn't wearing any clothes, or something similar. You shouldn't have any worries about talking to them then
Try to use standard phraseology when required. If there's nothing standard for what you want to say, just say it in plain, simple English.
And if you find yourself in the London area sometime, drop me a note and you can come and visit us at London Centre and we'll buy you a coffee and show you how friendly and well balanced all (well most) of us are.
WF.