@kedawa
As zipper said, if the plug has a metal screen on it, it can short out some of the pins if not inserted precisely. However, those plugs aren't that common, and I've never seen one on a joystick.
Electrically, the risk from hot-plugging is that there'll be a voltage spike or surge as the device powers up which can give abnormal or unexpected signals on the other lines. This could, in extreme cases, destroy input or output circuitry like the CIAs. However, a standard "dumb" joystick doesn't *actually* do anything electrically until a direction or fire button is pressed, and even then, doesn't use the +5V normally at all, so there isn't really a risk from hot-plugging them at all.
