>>89092833"Manko" means vagina/cunt in Japanese, so it's not something you normally say in polite situations. You only use manko in porn and hentai. So when a bunch of gaijin show up in chat, and they start posting "panko manko" it sounds crude. The majority of English speakers don't get this, they just think "panko manko" is a funny rhyme, they don't understand that it sounds offensive to Japanese speakers.
So basically, viewers need to avoid saying "panko manko" in Japanese chats. In English-only chats it's maybe okay, but not in Japanese chats.