Since moving to Europe in 1999, I've no doubt made more blunders than I can count. Probably many I don't even know about.
One that I do remember happened a couple of years ago on a bus in Brussels. I was one of a handful of passengers on the bus as it was stopped at a busy intersection. Just as the light turned green, a Dachsund belonging to a perfectly dressed and coiffed middle aged lady on the sidewalk escaped its collar and bolted under the bus. The lady froze in horror.

"Wait!" I shouted at the bus driver in my best expat French. "There's a dog under the bus!"

Only I was so agitated by the impending tragedy that in reality I had shouted "there's a dog ON TOP OF the bus!"

That would have been quite a feat for a dachsund. At any rate, the bus driver paid attention to the urgency in my voice and not the incorrect choice of words and slammed on the brakes. The doxie bounded back onto the sidewalk, his owner scooped him up, and the bus proceeded on its way.