I had set up my keyboards the night before a major gig at a local bar. I showed up the next night (OF THE GIG) and the drummer and bassist told me, "Oh hey, after you left yesterday we stayed and did some jamming. There was a girl who wanted to sit in on keyboards and we didn't see any harm in it."
Thankfully nothing got messed up with my setups I had spent hours arranging for the gig.
As it turns out, the "girl" was a local pro who happened to be a friend of my brother and who actually knew the tech.
She was insanely jealous of the Nord Stage 2, especially.
Small blessings, but I never want to hear the words, "we let someone play your stuff" EVER from a bandmate.