Is it dangerous to leave rubbing alcohol in your hair over night?

Not really: I don't know what you mean by dangerous and do not know why someone would want to leave isopropyl alcohol in their hair overnight. I can only imagine that by doing so, it would cause excessive dryness of the scalp, which is not a good thing. But as far as actually being dangerous, I am not absoluteley sure, but as for me, i wouldn't do it.