That tells them the right-wing bullshit mass email they are about to forward to you is, in fact, bullshit before you write them back and tell them -- and add "stop watching FoxNews you look like an idiot" causing hard feelings all around.
This is the App to handle the matter.
Of course, the first time this happens there are two possible scenarios.
1. They freak out and think the black helicopters are after them.
2. They call you to badly describe the problem for you and expect you to use your barely passable IT skills to fix the problem and tell them there is an "any" "anykey".
So I guess you can just block them.