I heard something very similar on local radio this week. A guy with his girlfriend were off to a wedding, stopped for petrol, got into some disagreement with a bloke at the petrol station. They drove off and thought nothing of it. Only miles later did they realise they were being followed, they stopped, the guy following them got out and shot dead the other guy.
You never know what nutters are out there, only too happy to do your harm for the slightest of reasons.