Sounds like you've been hit with a few too many lifted grounds on stage.

After a few, it can cause permanent damage.
What do you mean 'let me' test the power. I don't ask. I plug in and my outlet tester is ALREADY testing. And yes, I've told sound engineers when the power isn't wired correctly and made them run a different line from a different location. I've also told them when something was lifted and the mics were causing shocks, because only an idiot will knowingly play that way.
I've been working this way for DECADES and have never had a 'club owner' say boo about anything.
You know what's tacky? Getting killed because of bad wiring in a club.