What's the worst experience you've had with your tarantula?

I remember one time I was adding more substrate in my T's enclosure she's a curly hair named Gias. Tried to place her into a container but she opted to sit on my hand. Which was fine she was being very calm, so while I held her my mum placed her substrate in. Anyways eventually got her back in. She never flicked any hairs or nothing. But my left arm just below my wrist started iching like crazy. And when I say crazy I mean I scratched it so hard I made it bleed, still have the scar. I'm use to her flicking hairs but I've never had a reaction that bad before.