If you tell a truly inconsiderate person that they’ve been rude, they will sincerely deny it. This is why we call them “inconsiderate”; they habitually fail to consider or even realize how their actions affect others.
If you respond rudely instead, then over time they will begin to recognize, either consciously or subconciously, the Pavlovian connection between their own inappropriate behavior and your negative response, and they might learn. If they catch on and say, “Why are you being rude? *I didn’t do anything [this time]*,” then you can respond with, “Well neither did I.” 
Justification: the truly inconsiderate do not have a respect for the social contract. They live by the “me first” code. Of course, this wouldn’t work if everyone tried it, but even though they’ve been told this, they stoically await tangible proof. Showing these folks what it would be like “if everybody did” provides them with the undeniable scientific proof they seek. (I was quickly cured of my inconsiderate, “me first” thinking by someone who rewarded me in kind of a minor rudeness. It was nothing nasty but I took the lesson to heart and it changed me permanently.) Also, you have no need to fear karma as long as you don’t go above and beyond what is called for, and as long as your rude behavior is calculated to do more good than harm. (Read carefully)
One final note of warning: if you do try to use this technique, have a strategy in place to avoid hours-long discussions about the minute difference between their rude behavior and your negative response, that one, all-important difference that makes their behavior completely acceptable and condemns yours.
