And thats why you guys are working with computers and not people, cause that's pretty rude. What they are doing is only rude if they are aware that it annoys people. You response is rude nonetheless since it's a version of "that'll teach them" which is a pretty immature way of handling disagreements or conflicts.

A more mature way would be for "first offenders" to politely reply hi and help them with whatever they need and then when everything is done politely point out that asking directly would be better next time, perhaps with a link to some version of nohello.net. With "repeat offenders" sure, go ahead with what you are doing.