Long ago and far away, a man got the crabs. He itched and scratched and as so very miserable. When the next door neighbor came to see what was going on, the poor man said, "I have crabs, so, I'm crabby"
That's how it all started.
Oh, maybe it was the fisherman who caught a bunch of crabs that got out of the bucket and got all over him.
When his fellow fisherman asked what his friend's problem was with the crabs, the fisherman said, "Im crabby"
Actually it's all a lie. I have no idea how crabs got a bad rap.