When I saw the title, I thought you were looking for universal constants like "It's always in the last place you look", or "You never have the right change for the meter", or "Never wear ugh boots outside the house"

But you want physical constants. That's not interesting. I mean, they were lying around just waiting for someone to notice. The ugh boots constant required painful research (by someone else, thankfully).

Hmmm. I was going to quote something educated, like Feigenbaum's number or the universal gas constant, but the only one I can really remember is that the phone number of the local pizza place is 131888. Somehow that number was always involved in a late night physics assignment.