Hmm, the cockateil on a leash and harness is definitely a top contender. I mean, there just seemed like so many potential ways for that situation to go badly. Aside from the risk of letting go of the leash, it only takes one jumpy dog and the bird becomes a tasty snack.
But another top contender is the couple that decided to transport two piglets in a plastic box, with a lid, and no air holes. Yeah, the RSPCA had a chat with them.
I recently bought two peppered cockroaches (very large tropical roaches) from someone who had taken them to a ComicCon to show off, and who was not expecting to sell them. Transported the roaches home in a (cardboard) business card box held shut with a piece of Gorilla tape, with some moss inside, closely watched the whole way to be sure they didn’t try and get out. They didn’t. I wouldn’t do it again on purpose, but it worked!