I don't think those 'jokes' go over as funny as the people that may make them hope. If everything my manager said was jokingly prefixed with 'you might get fire

I don't think those 'jokes' go over as funny as the people that may make them hope. If everything my manager said was jokingly prefixed with 'you might get fired...' well, I'd consider it annoying and not at all a joke. If it's used sparingly, I'd take it seriously. Either way, I'd certainly feel like I'm walking on eggshells at that company. It would not improve morale at said company. Put it another way - your wife, when you get home always says "You are cheating on me and I know it!" and then plays it off like a joke... this goes on every day... would you find it funny?