My friend is a dangerous driver what can i do?

Don't get in a car with him. Seriously, if you don't feel safe then don't do it. Be polite about it though, say thanks for the offer but you've got another lift somewhere and I imagine he'll take the hint. If not then, he'll have to get offended. You've gotta put you're safety first and hopefully by him realising people are scared to get in the car with him will make him get his act together. Don't let him bully you into getting in the car with him.