I was once had a conservation with a friend consisting of a planet populated only by budgies, aptly named Budgie World.
There were two types living there. The blue budgies lived on the sea...somehow, and the green budgies lived on the land. In place of the Moon there was a giant birdfeeder orbiting around the planet. And every so often cats from Mars would charge down into the atmosphere and keep down the population.
Not THAT weird really, but that's the most recent one.
There was a favourite of mine. The conservation started when we saw a beetle fall off a wall, get up and was completely unharmed, whereas a human falling an equal distance would turn into mush. To this day I have no idea how, but that led to an intense discussion on China and World War Five.
OT: Yes, weird convos are awesome.