An LED is a Light Emitting Diode. The key part of of that name is "Diode." An LED is a diode. Diodes do not limit forward current very well. The extremely steep current/voltage curve (an exponential curve) is probably their second most important functional characteristic which results in sales of diodes.
When you put a forward voltage on a diode (an LED, BE junction of a BJT, or whatever), it's current DOUBLES with each incremental 25mV of voltage. So if you applied 0.7V (700mV) and got 50mA, then you should get about 100mA at 725mV, 200mA at 750mV, 400mA at 750mV, and so on. So what would you expect at 20000mV? The theoretical answer is about 6 times 10 to the 230th power amps. But your home's circuit breaker (thankfully) limits current draw to something less than Bazillions of times the total power output of all generators on planet Earth. Your LED draws maybe 20 amps for a few microseconds, turning a very small volume inside it about as hot as the Sun, and then it is all over.
If you do this with larger parts, the shrapnel can kill you. An electrian at a factory I worked at, had the misfortune of crossing two phases of industrial strength AC with his screwdriver. As far as could be figured out, he was not electricuted: the plastic screwdriver handle protected him from that. However, the short instantly vaporized the metal in the screwdriver. The resulting explosion killed him.
So provide external current limiting in line with your LED, or... wear safety goggles.