LOL I've actually done exactly that. A friend of mine was driving a a huge huntman crawled from her side window, over the dashboard toward me, I literally opened the door and jumped out shreiking..... Luckily enough we had just taken off out of a dirt car park, so it was barely moving.... Hate to think what i would have done if we were on a freeway.
I once got off a speeding fine because there was a huntsman on my drivers side window and i was freaking out. whoops. The officer was kind enough to pretend the spider was on my shoulder. I jumped out and spider danced like ive never danced before. I don't think ive ever heard anyone laugh like that before.