I'd imagine that putting them under a reverse bias of any significant level in excess of the power rating would do a pretty decent job of buggering the N/P junction in the diode too. Conventional diodes (that is, purely electrical, and of the semiconductor diode type, obviously there is no P/N junction to destroy in a vacuum tube diode, although these are not common nowadays, most being semiconductor diodes, the LEDs are, as are both conventional electrical diodes and those users for laser applications, which are often based on gallium arsenide, a compound of the elements gallium and arsenic) can only handle so much, which is obvious from the fact that different ratings are available for different applications. (essentially a regular diode being operated, wrongly, as if it were an avalanche diode, and the resulting reverse-biased avalanche breakdown permanently wrecks it)
Diodes are, essentially an electronic one-way valve, designed to allow current to pass in one direction and arrest it in the other. Used for such applications as for arresting back EMF such as when sending an electric pulse through a pair of electrodes connected by a conductor which is in contact with (or in some applications , like plasma railguns for example, partially vaporized by the current dumped into it forming a conductive plasma, the plasma acting both as a conductor, and being ionized gas, plasma pressure itself, forming behind the projectile, serving to push forward the round in a plasma railgun) and which then moves out from between the electrodes, if the current is thus interrupted, a back-flowing EMF spike ends up headed towards the power supply which can make a mess of things, especially in the case of say, something like a high-energy, powerful marx generator being used as a pulsed power supply and electrolytic capacitors being used, as electrolytics are polarized and subjecting them to reverse bias damages the dielectric (and needless to say, you go and blast many farads worth of stored energy at hundreds of kilovolts or more through the railgun, the resulting backwash, if allowed to reach the power supply and not be arrested before it gets to the cap bank the Marx generator is made with is going to worse than just damage the dielectric. Never done so but I should think it would blast the caps to pieces)
Which again, quite obviously is not what you want your face anywhere near when your eye is up against sight, taking aim
, and quacks like a 