Pistol on coat-hook: To me, the most plausible version--
Years ago, I read an account by Mas Ayoob where he wrote of an officer who hung his 1911-style pistol on the hook, and bumped the trigger when he tried to lift it off. The pistol fired (the safety obviously having been knocked off) and the officer jumped, bumping the trigger again. I think that only two shots were fired, but it's been a while.
I seriously doubt a properly functioning 1911 would go off unless the grip safety was deactivated. I could see a Hi-Power going off multiple times if the safety was off. I doubt any DA to SA pistols would go off since the trigger pull is heavier and longer.