I very rarely give into reciprocating rage with yelling anymore because that's exactly what the other driver wants from you. If you don't have issues with escalating the situation higher because you are one upping them and not giving them 'rage', you can do one of two things that ALWAYS infuriates them even more.

1) Laughing, which you have already stated.

2) Yawning. Look at them, let out a big Yaaaaaaaaaaaaaaaaaaaawn and use your hand to "cover your mouth" to emphasis that what they are doing is boring the hell out of you. I can't tell how this really gets their veins in their neck popping