I proudly announced to my german roomate’s family that my father worked for a firm involved in the supply and distribution of narcotics across Europe.
Turns out “drogen” is (illegal) drugs, whereas I wanted “medikamente”, meaning pharmaceuticals 
Ich bin heiß = I am horney
Es ist mir warm = I’m hot
Conversely, when I first moved to Chapel Hill, I kept hearing people talk about Dean Smith in reverent tones. I spent about a year wondering what he was the dean of.
My dad said that in his freshman year at MIT, he was buying a Coke, and the cashier said in a thick Boston-area accent, “You want a bag for the tonic?” But with the accent and the terminology change, he had ask for a fourth, embarrassing repetition before he got it. I’ve still never heard “tonic” for soda-Coke.
I once saw an English-language job ad of a German company, giving the region where the person was to work as “Europa”. Might have been an attractive offer if you got your travel reimbursed and got to keep the frequent flyer miles…
I was in Tijuana shopping, drinking, and practicing my sad Spanish. In one shop an assistant went into the back room to find something for me and another shop assistant asked if I needed help. I meant to reply that I had already been served; instead, I said that I had farted.
On the same day, I told a waiter at a restaurant that we were “tires” instead of “full” (llanta/llanto).
On a later trip to Mexico my mother wanted to buy something in a shop and assumed that the latina in the shop was the salesperson. Very loudly and slowly she asked “Do yooooo speeeek Eeenglish?” to which the woman replied “Lady, I’m here visiting from Los Angeles.”
Not so much faux pas’es, but a grappling with regionalisms here in NJ/PA:
It took a few times to understand that “war’dur” = water
Same with “dar’dur” = daughter
“Down the shore” = “go to the beach”
No one here knows what an “elastic” is (rubber band)
“War’dur eyez” = Italian slurpy-drink
Tomato pie = pizza with nuthin’ on it*
*And, asking for pineapple on a pizza is treated like a mortal sin. Can’t help it, I’m from California.
Hah, go to the other side of Pennsylvania and they call a rubber band a “gum band” - go figure.
Hmmm… I’m from Tre’un, and don’t quite hear these. I never picked up the accent (at least people here are shocked that I’m from NJ). I remember hearing “wooder” for “water.” No “R” sound (other than the end of the word) that I recall. Same with “dawder” for “daughter.” I do remember reading the Fluffya Inkwire (Philadelphia Inquirer).
Joe
FYI: faux pas is already plural.
When you go down the shore, please don’t act like a bennie.
I’m from New Jersey, and most of these strike me as pretty weird, except for “down the shore”, which is the correct and proper way to say “at the beach”. "Tomato Pie’ was already pretty archaic when I was a kid, and i haven’t heard it in NJ since the 1960s. As for pineapple of pizza, that’s part of a Hawaiian pizza 9minus the Canadian Bacon), which has made inroads into the wilderness of NJ even before California Pizza Kitches came around. you must’ve been pretty far out in the boonies to get odd looks – we never have a problem with getting that. Heck, they even sell it at the pizza places Down The Shore.
I remember an old episode of David Letterman where he had Nicole Kidmann on.
She somehow ended up explaining how in Australia they use the term “crack a fatty” to describe getting an erection.
Letterman (and most Americans) had never heard this term and since Dave found it amusing he kept slipping it into their conversation to make her blush and gasp.
“We’ll be right back after this break while I go crack a fatty.”
“After the show I like to go home, relax, and crack a fatty. How about you?”
Years ago I was a fish out of water - a Texas girl in NYC - and I was missing me some Tex-Mex. I talked my friend into going to a Mexican restaurant. We were seated and served chips with a thick green sauce and a red sauce. I thought the green stuff was guacamole, and took a big ol’ bite. To my chagrin, it was a salsa verde that was screamin’ hot! I drank my water as well as my friend’s water, followed by a beer. I looked like a dumb-ass. 
Maybe it’s the part of NJ I’m in, or the pronounciations are some beastly hybrid of PA-NJ? (I teach in Eastern PA). Or, maybe my West Coast earballs are hearing something different?
I can assure you that here in Tren’un the “tomato pie” is alive and well; four pizza restaurants within a few miles of my house have banners and signage with “tomato pie” and the prices. I’ve had several comments at pizza places when about “ruining a perfectly good pie” with pineapple.
Mmm! Crab rangoon! Best served with a sweet chili sauce, it’s another American Chinese classic.
Once, when I was in New York City I asked a pretty waitress in a restaurant “May I make love to you and impregnate you?”. She slapped me in the face. I forgot that that means something completely different on the other side of the pond. Boy was my face red.
My husband’s family are from Yorkshire. One of his aunts asked me if I would like my tea in a pot or cup. Thinking it must have been some sort of northern joke, I answered, “In a cup, of course”. Turns out that in Yorkshirese, “pot” means “mug”. His aunt disdainfully handed me a china teacup and saucer while every-one else drank out of mugs. Fifteen years later, they still regard me as a stuck up foreigner.
wooder ice is not a drink. Unless you wait that long. It’s flavored shaved ice scooped into a cone. And it’s lovely.
I’ll have to try it this summer. It doesn’t sound that appetizing, but then again custard didn’t either (mmmmmm, custard ice cream!)
There were a lot of Indian students in engineering at the University I attended. On the first day of Advanced Mechanics of Materials, an Indian girl walked by the desk where I was sitting; she was cute so I smiled and said hello. She gave me a big smile in return, leaned over and whispered, “Do you have a rubber?”
Turns out, she meant “eraser”.