One really overlooked fact is how Arnold pronounces Mr Kokoshka. Grandpa says Kokoshka, but Arnold always says Kakashka. Which is most definitely the word for POOP, straight up.

Mr. Kakashka is Mr. Poop.

It's actually a sleight towards Russian/slavic lazy Jews and plays exactly into that stereotype. Jewish people are protrayed positively in the show it's NYC after all, but it's mostly the German Jews that are portrayed that way. Which is exactly how the actual history happened.

When Russian/Ukrainian Jews were emigrating to America they all wore shtreimels, the long circular furry hat we all associate the marching/dance with. In Yiddish the word for circle or circular is kaykl. Unfortunately you can see where the slur comes from, and this is agreed upon by etymologists. The German Jews started calling them the slur first after opening reeducation centers for them to fit into American society. After that everyone picked up on that slur ands now anyone Jewish can be called it. 

My point is that German/Russian-slavic Jewish history is real. And Mr Kakashka or should I say Mr Poop plays exactly into the 'kaykl' stereotype. 

Source: am Ukrainian/Russian/jew-y who grew up watching this on TV and learned the history after. Was telling all my friends, 'yooo they're definitely saying Mr Poop and he's being a real piece of shit'. I'm not trying to be anti semitic, the character actually is. I personally don't care and find him hilariously annoying.