Beetroots are an old colloquial Polish term for boorish uncultural people. It is mostly used as a noun - a person is called a beetroot. Onion is relatively new and is used as an adjective meaning onionlike or is further developed into nouns - onionship means behaviour. Onion pies or eaters are also possible.
Onion pie looks like a mini pizza with a lot of onion on it.
These terms are used by Poles about other Poles whose behaviour is unacceptable. There is even a rhyme - Polaki cebulaki.
Examples: Dad, where shall I put the rubbish? Behind the wind screen.
Dad, I am bored. Intelligent people are never bored.
No need to have a shower, we are going to the swimming pool.
When I went to a traditional historical event in Krakow attended by hundreds of visitors, I was amazed to see only one bottle lying randomly in the grass and all the remaining rubbish diligently stored in and around bins (unfortunately, completely full by 3 pm) in the area.
So, girls and boys, if you look for cultural partners who care for environment and other people`s feelings and tastes and are interested in various other things than TV and pub crawling, you should definitely participate in such events.
I wouldn`t advise you to look for such a partner in other places and events, e.g., on Wisła banks in Warsaw, after the new law allowed drinking in the fresh air there.