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By the way, I wasn't aware that creepers could instant kill if you had armor on. I haven't been killed by a creeper for a while, even with no armor on Magic Farm hardcore.
It's very hard to get killed by one, but if your hand slips and you fail to back away, you'll take tons of damage. Most people have the reflexes to move back from a creeper if it's about to explode, but if you're in a 1x1 hole, and a creeper falls down and explodes, it can kill you easily. Supercharged creepers challenge nano/quantum armor if they explode right next to you, though they're obviously quite rare, and you shouldn't be in a 1x1 hole anyways.
EDIT: Also, they have lots of knockback. If you jump at the right time, you can get launched 10 or so blocks into the air from a creeper. I think supercharged creepers have a bigger knockback, but I'm not sure.