"Punish those who don't want to be his friend? That doesn't sound very friendly to me.
Oddly enough after first viewing the official slender man thread, the next morning my microwave broke, and then a few moments later a electronic thermometer turned on for no reason a few feat away. Then I read more about him and I find out he could potentially mess up electronics.
And then what ever it was started to invade my mind, and I was able get rid of it.
When I fought it in my mind I made lots of mental clones of myself (before attacking), and all that were injured from the battle seemed to be infected with something.

It could have just been insanity, it could have been the slender man.
Either way I would recommend not giving into fear, Maybe try to cleanse your mind somehow. Just don/'t go into mental combat against it, unless it is truly necessary.
Also, there are some rumors that the Tulpa Effect (basically enough people believing made it reality) created the slender man.
Some others claim the being gets stronger the more believe it,
And then there are the ones that say it has always been here, and the tulpa effect has no effect on it)"