I had a guy do the same frikin thing two days ago in a Denali. I was so pissed at his ignorant dangerous ass driving. Fortuntatly I was in my moms convertable so I could give him the appropiate gesture... you know like Hang up the phone, and concentrate on driving since you obviously can't do both at the same time.
He didn't know where the f*** he was going either which was really pissed me off.