I was about halfway through my second playthrough of Half-Life 2: Episode 2, on Hard mode, trying to get the gnome achievement. I got to a building, placed the gnome carefully on the car, and set off into an abandoned house to open a gate or something.
Walk in, hear a noise. The hunters are here. Equip shotgun, and start blasting away. Two hunters down, out of ammo. Quickly slam 'G' to pull out my Gravity Gun, and pull out every explosive barrel I can find, hurling them at the aliens. Run out of explosives, dash back into the house, chug some health packs, and hide, thinking.
Split second decision. Whip out SMG, and run through about 3 of the guys, occasionally peppering them with bullets. Get out of the warehouse, and look at car, the gnome still perched on the boot. Smile. Jump in, reverse, watch gnome fly over windshield, and face hunter a couple of meters away. He fires flechettes, I slam down on the accelerator, the darts blocking my view, and drive straight into the combine freak. He tumbles over the car, falls lifeless, and I dive out of the car just before the flechettes explode. Then I turn around, and look at the other hunters.
I get back into my vehicle.
...And that is the ridiculously awesome tale of how I learned you could one-shot hunters!