I can’t tell if this is ragebait, you’re just trolling, you’re genuinely unaware OR if I have missed the moment when this flag’s meaning got reclaimed

Es ist kein Slang sondern Dialekt. Ein plattdeutscher Dialekt um genau zu sein, ich kann dir allerdings nicht sagen welcher.

Hope it helps, if you don’t understand some words in my answer feel free to ask, I can also add an English translation but I thought you’d probably like to try and understand an answer in German.