you'll hear different opinions on bristleworms... Some say they are safe up to about 6" long, after that they should be removed cuz they can be dangerous to smaller fish...
That said, I have one in my tank that is 18" long =)
oooh I hear ya there man... I was extracting a tang from my tank the other day (gift from a friend when he had to break his tank down, the tang proved far too agressive for my tank and he pooped WAY too much) and I found one of my big ones the hard way! Those stinking bristles STING =\ I bathed it in peroxide as soon as I got the tang out, cuz you gotta watch out for infection in those conditions... Fish tank conditions aren't exactly sterile
Ouch. Never got stung, but I hear it 'aint too comfortable. Vinegar is supposed to be good to neutralize the venom. Pissing on your hand is supposed to work too, but I'd opt for the vinegar myself.