I have more of an issue with some of the comments here than his rudeness to be honest... he was just a prat because he was either too stupid/inattentive or just plain ignorant to notice us, or just didn't care.
Some of the responses here are worse, because even with time to consider, some of you still think his behaviour is acceptable to some degree or that it doesn't merit further comment and that I was being over the top in reacting with a choice insult.
If someone insults you, you react. How you react is up to you, but you should at least show your displeasure in some way. How I choose to show mine is indicative of the world I work in...
Unless you like getting used as a doormat, in which case carry on...