We all know the theory about the Chinese Water Torture. It isn't the water dripping on your head that drives you insane, but the constant uncertainty, the relentless waiting for the next drop to fall.
The same theory can be utilised in your day to day interactions to drive someone into insanity, in such a way that nobody will ever blame you - you won't even have to feel a flickering of guilt, because each individual action you take is completely reasonable, or even considerate. It is only the sum of what you are doing which serves as torture.
First, pick your victim. There are only two real requirements here:- first, that they should be relatively organised in their own day to day life (this method cannot be used for destabilising anyone who is wildly unpredictable); the more organised the person is, the quicker this method will work. Secondly, they should care about you. Good friends, or better still ex lovers, are a prime target.
Step One: The Set Up.
Before you do anything else, it is absolutely vital that your victim should be made aware of your fondness for them. Their problems are your problems, their celebrations are yours. Hug them, laugh with them.
Get into the habit of seeing them on a regular basis. Don't make firm arrangements, but see them on the same day every week, or at the same time every day. Allocate your time carefully, so that you never have quite long enough to talk through anything serious or important, unless the problem is yours. However, don't let that stop you starting serious conversations. The end of this stage comes when you are in the middle of talking about something that is clearly important to them. Dash off, with a hug, and say "I hope we'll be able to finish this tomorrow/next week" -- That "I hope" is vital. It sets up an expectation, but makes no promises.
Don't see them for a month, if your meetings were weekly or a week, if they were daily. Next time you see them, greet them exactly as usual, but perhaps drop in a comment saying that you're sorry you haven't been around, but you have been very busy. Other than that, act completely normally.
One day, dash in for five minutes, give them a hug, and dash out. The next time you come to see them, make it a completely unexpected time, and stay for twice as long as usual. Leave them unsure as to when they'll see you, and for how long, but say you think you'll be around at foo or you'll try to be around at bar. Turn up a few minutes early, an hour late (if you can guarantee they will either be waiting, or someone they know will see you), or not at all. Be completely inconsistent in how long you stay. Call them, several hours after you should have been somewhere, preferably when you know they'll be out, and leave a message on their voicemail apologising, or drop them a mail. When they reply, ignore it. Whenever you do see them, be open, friendly and glad to see them.
By this point, your victim will be confused and angry. Encourage them to express their frustrations to you. Take as long as is necessary for them to say everything they want to say. Be understanding, apologise for upsetting them, make quite clear it was unintentional. Remind them, in passing, that you never made any promises. Reiterate how much you care for them, several times.
Repeat steps one - four once, and then steps one-three.
Pick a time to see your victim where you have absolutely nothing else to do. The masterstroke is a wonderful way to relieve the boredom of a Sunday when your other friends/partner are out of town. This time, when they express their upset, take much longer to listen. Agree with everything they say about your behaviour. Promise them faithfully to try harder to be there for them (remember, promise to try, not to do it). Give them lots of hugs and support.
Disappear totally, for at least twice as long as you ever have before. Don't call, don't mail, have no contact whatsoever, except maybe have someone you both know say 'hi' to them. They almost certainly won't contact you at this point, because they know that you won't get round to returning their calls or mails.
Out of the blue, turn up and say "Hi, I've missed you." What you'll find will be a gibbering wreck or an automaton.
Congratulations, you have been successful.
If anyone thinks I am seriously advocating this -- shame on you!