A stock phrase, almost impossible to use nowadays without making fun of it. Commonly associated with Dont Make Me Take Off My Belt, but by extension may be used mockingly by instigators of Cold-Blooded Torture or the Jack Bauer Interrogation Technique. If they're of a more honest persuasion, they may invert it as "this is going to hurt you a lot more than it hurts me". The original idea, of course, is that the speaker doesn't want to hurt you... in fact it causes them psychological pain just as bad, if not worse, than your physical pain... but they feel that they have to do it for your own good. In other words, they're the real victim here. If used straight, it's almost certainly an example of Why Did You Make Me Hit You?... but it's not used straight very much nowadays.
Hello, Unknown Troper. You'll need to get known to lend a hand here.