I think I might already know the answer.
I went to a work do - a fundraiser thing. Towards the end of the evening, when everyone was swapping tables and lots of people on the dance floor, a colleague came and sat down at our table - she sat down and looked at bit horrified at my two empty cans which I had squashed when they were empty. She said, "who's been crushing cans??!" and it was noisy and immediately the conversation moved on, but it was me! I had squashed them. Is that a horrid thing to do? I didn't know.
I mean, obviously I don't imagine the queen crushed cans at state banquets. I wouldn't do it at MIL's fancy Christmas dinner table. But is it so horrid that I should not even have done it at a rowdy work do with paper plates and drinking from the can?