Why are pirates called pirates?

'Cos they Arrrrrrrrrrr!

Yeah, I know, I know, it's old as the hills, but it seems to be my hubbies favourite joke and my team leader at work has been known to tell it on more than a few occasions too!

He (my team leader) had a cut on his finger today, so my colleague Jacqui (of bling fingernail fame) whipped out a pack of pirate plasters from her drawer and proceeded to wrap one round his poorly finger. I mean after all, isn't that something every office has lying around?!