Nope. Couldn't fake any form of accent if I tried. It would just like I'm mocking someone.
I have, on very slight occasions, said as few of words as possible in a conversation,just to not bring attention to myself (though always in my American accent, because I suck at accents) But no one gives me sh*t about being American- either that, or I seem to unconsciously let it roll off my shoulders.
rynn, that same situation could have happened to anyone, the person before you, the next person in line, who could be British, or Polish, or American, Japanese, whatever. Not like the scanner was like "Oh an American, lets act up" and if the cashier was running around to help you, then all is fine. I guess what I'm saying is, stupid things happen to all of us- where ever we are and probably wouldn't have mattered if you said sorry in your American accent. I personally wouldn't have worried about it, but if it makes you feel better in an uncomfortable situation, then that's ok. I would just take heed and make sure you're not going overboard and it looks like you're mocking someone.