I worked in a US office for a while (but with a few other British people as well). I didn't feel the need to edit my sense of humour luckily, but I purposefully switched to saying things like "sidewalk", "elevator" and "bathroom" because it made interactions a lot easier.

I'm American, but I've said "washroom" for a long time because I'm not asking to take a bash, but at least I wash at some point afterwards. Most people seem to understand fine, but I do get a few now and then.

Funny story, I was visiting Hong Kong one time, and asked the young waiter, who seemed to speak English just fine, where the washroom was. Blank stare. Bathroom? Cesuo (Mandarin)? All blank stares. I was a little out of options at that point... Turned out the word I was looking for was "toilet", which is a word I never use.