Rotting onions do stink.

It seems to be a special trick that onions do, to rot from the inside. So the outer copule of layers of the onion are fine, but then there's two layers of mushy brownish stuff, then the onion's core is fine again. You can't tell if your onion's rotting without cutting it open. This can be super-annoying if it's your last onion, because I don't care to use rotting onions.

With respect to tears: my daughter adopted the practice of slicing onions while wearing swimming goggles. I think she was about 12 years old when she first did that; she's 35 now, and is still doing it. She looks a hoot, but looking daft is better than suffering. I think I've developed immunity to sulphenic acid myself.