Deadly Details: A magnet cannot really hurt you. However, get a magnet powerful enough and it can destroy anything. Magnets do not just attract iron, they attract every matter. A strong enough magnet can attract even plastic, or an even more powerful one could crush an organic being like a lion or a human into a cylinder shape. Luckily, it is impossible within the current realm of existing science to have such a powerful magnet. And if a magnet powerful enough to kill a human did exist, it would probably destroy all life on earth as we know it long before it killed just you. Fortunately, you don't have to worry about dying from a super-powerful magnet - at least, not instantaneously.

Deadly Details: A theoretical celestial anomaly, a quasar is the supposed ejections from a supermassive black hole that shoot out light, x-rays, gamma-rays, and every form of matter possible, near the speed of light, out of either side. Get in the path of a quasar and it won't just kill you, it will obliterate everything. Luckily, if it ever happens we won't know what hit us - the entire planet, possibly even solar system, would be wiped out instantaneously. You won't have to worry about one of these hitting you. If it does though, you definitely won't feel a thing.

Deadly Details: Something I came up with based on my knowledge of quantum theory. Theoretically, if the quantum matter throughout the universe was aligned just right, it could result in waves that would obliterate the universe. If it happened, then you'd never know it because the whole universe would be inverted and reverted in a fraction of a second, wiping out all life and all matter instantly. We can safely say this probably isn't going to happen to you.

Deadly Details: Many scientists now believe black holes may not even exist. However, if they did, getting caught anywhere near the event horizon is an accident waiting to happen. You wouldn't just get sucked into a black hole. It would disassemble you atom by atom tearing you apart. While you might survive without an arm or a leg, there is no escaping a black hole. In moments there would be nothing left. Fortunately, you probably won't feel a thing. Probably.

Deadly Details: Suppose that a celestial explosion such as the collapse of the Sun which went supernova, binded together additional electrons onto every atom within the entire solar system with a massive explosion that puts nuclear explosions to shame. Theoretically every atom in your body would be transmuted into another material, much like transmuting coal into gold. Sadly, you won't be able to walk around like Gold Man, because you will only be transmuted for a millisecond before being vaporized with your atoms strewn across the whole galaxy. Cool way to go, if you ask me.