Yup, a very good question. Here are steps you could take if the person ahead of you is "lazy" and does not give way:
Take down his plate number.Find out from the Maroor who the driver was and his/her contact details. Call him or her and give him one of your "valuable" advice on how to drive.
Listen to the reply p-a-t-i-e-n-t-l-y. And if the other side is a lady, don't be surprised if you get to feel the length and strength of the stiletto.