I would bet that at least some portion of these are genuine (failed) attempts at camraderie or playful banter. But much like the cashier-jokes ("no tag, must be free") I bet it becomes really grating after a while. It's probably a novelty to see someone unicycling, but it isn't novel for the rider.

I kind of associate these types of failed jokes with a particular type of awkward middle aged-to-older dude who accidentally puts people down when trying to be funny.