What you are referring to is called Black Dog Syndrome, and there's a debate over whether or not it's real. A lot studies don't show it to be. It may be one of those things where it's generally believed - even by people who work at shelters - but it doesn't pan out. I know a few nurses who swear by the full moon stuff (more injuries, births, etc.) even though the numbers show that's not true at all. Or in short: confirmation bias.
To be fair buses in the UK seem to have a mandatory 'fucking-mentalist' policy. If there's not some crazy person who smells of piss either being annoying, weird, or aggressive (or all three) then you feel like something isn't right.