As a newcomer in the United States, I have made many cultural gaffes. Some were not such a big deal, some were mildly embarrassing and some were, well, quite painful.
When I first started working in the U.S., I followed my boss into the restroom one day. There were five urinals and all of them were free. He went to the one at the far end. I wondered why he didn't go to the one that was closest to him. I chose the urinal right next to him. Standing beside him, I said, "It's a nice day today, isn't it?"
He didn't respond.
"Nice day, isn't it?" I repeated.