<human>: Give me the gist of the text in a nutshell

As mentioned, my SO has some severe road rage.  If someone in front of us is driving like a dick, he will not only match that but escalate it to a point where it's gotten physical in the past (according to him).  It's not a rare occurrence for us to be driving in town and the window is rolled down because he's screaming at someone next to us.  I've seen him lose his temper at complete strangers, lets them engage his anger for the smallest reasons... but he backs off as soon as it comes to getting out of the vehicle.  At home, he has been nothing but stable in terms of temperament... it all comes out when he gets in a vehicle.  

It's a tourist town.  I give him a little leeway because tourists really do NOT know how to drive in this city, and it's quite evident when the city's population swells to twice its size.  However, it's basically a ticking time bomb and I'm at the point where I'm not opposed to him getting his ass kicked for acting like this.   

How do I calmly open this dialogue?  The only time I've ever tried is when it's happening, and I'm usually not speaking very calmly then.  
Does anyone else have experience with this?
<bot>: My SO has severe road rage.  He's going to get his ass kicked one day and I'm not going to stop it.  How do I talk to him about it?