Truth be told... Some idiot who had beef with me once, opened my tractor's fuel cap (key-lock for the cap wasn't working anymore) and poured salt into the tank!!!!
How lucky I was for the driver to discover it in the morning while he was checking fuel level, before the worse would happen!!! God loves me
So for this one, it is a prank of course, but I don't rule out some fool who can do this to your car (remember he can open the cap with a screw driver!!)