You could always try the "smile, nod, change the subject ASAP" approach... A buddy of mine can be like that, he's a great guy and incredible friend but has moments where he can become the most angry and bitter person on the planet. If you don't bother listening and just quickly agree ( I generally try to not listen and just nod or say "yeah") and change the subject, he not only shuts up, but will start cheering up and talking along with whatever is brought up instead of ranting and raving about whatever angered him in the first place. This approach also seems to keep him in a better mood and from going on his usual rants as often.
Of course, along with NotesMaeve, I'm the king of rampaging while driving. I don't know how many times I've been on the phone with my girlfriend when she hears something like "Yeah, my day's going well too baby, I love- you ***d*** f****** dumb a** what the h*** are you thinking!!??!!??" when someone flies out in front of me/runs a red light and I almost hit them... The area I live in has seen a housing development/population explosion while the genuises running the city haven't seen fit to exapnd the roads, so traffic accidents have increased dramatically and driving like a maniac has become the norm. This is just a horrible pet peeve of mine (there is really nothing short of delivering your pregnant wife to the hospital/saving the world that is worth risking killing someone else on the road with your crappy driving over IMO), and I tend to flip out over it. My poor girlfriend just listens, calls me crazy sometimes, and usually helps me stay pretty cheered up
