What's the stupidest debate/argument you've ever had?

The other day at work someone blurts out in response to what i don’t remember: “sharks aren’t fish” . . . then someone agreed and said they were mammals then someone refuted and said they weren’t mammals but they also weren’t fish. People kept trying to prove their point spurting out any animal fact they knew. 15 minutes two texts and a google search later the argument died down. By the end of it i decided A) sharks are fish and B) that it was the stupidest argument I’ve ever been a part of (a heated Disney princess argument being a close second). So I’d like to see if anyone has a similarly frivolous and or stupid argument and if so what about?
we as a group can bask in the fact that we as a people know so little about so much.