The name comes from how certain software companies portray Open Source and Free Software, and certain aspects of a lifes philosophy that encourags people to do exactly as they please as long as they accept full responsibility for their actions. In some cultures, it's seen as "evil" to think like that, but just because someone feels they can do whatever they want, it doesn't mean they automatically want to do bad things. Same thing applies to ESL.

Evil Software Licence
ESL, pronounced "Eh-zl"
Version 1, by Fredrik Vold
http://fredrikvold.info/esl.shtml

Intended use
While you do as you please with this licence, the intended use is for scraps of code that have little or no value. Things that anyone could easily write, but that it'd be easier to just grab from some website somewhere.
Most licences, even the most liberal ones, demand that you credit the original author and that you retain the licence. Who's honestly going to do that over 200 lines of Perl they've rewritten half of anyway? It's just not realistic to put tiny scraps of code in a huge project if it means you have to drag along the licence and all it's demands.
With this licence, that code would just seemlessly drop into the project, and it would be completely useful without any drawbacks what so ever, and that's what Open Source is all about, right?
Naturally, if you've worked for months, or even years on a project, and your next paycheck comes from it's success, it's silly to release under such a liberal licence. You'd want your name associated with it, at the very least!
ESL is all about free flow of little useful peices with no strings attatched. Think of it as Public Domain with a cooler name.

ESL comes in two forms, a short one, and a long one.

Short version
Do what you want with this sourcecode, but accept full responsibility for what you do.

Long version
For the licence to apply, the full sourcecode of the software must be readily available to the user.
Software licenced under Evil Software Licence comes with absolutely no warranty what so ever.
You can do with it exactly as you please, including using parts or whole of it in other software, even without crediting the original author. You can even change the licence, if you want.

If this software is good enough for you to use, maybe the original author deserves your respect? Credit the original author if you want, it's up to you! Especially if you had the software written for you specifically, it is generally a good idea to credit the author, as that author might refuse to work with you ever again if you "steal" the work.
Keep that in mind, when you do whatever you want with it. In a legal context, you're absolutely free to do exactly whatever you want. Your moral decicions are left to your self.

If the software breaks your system, or causes any sort of problem what so ever, you have full responsibility for it. It is your own fault for running software on your computer. If you run it on someone elses computer it is not up to the licence of the software to decide if you are to blaim for running harmful software on that computer, or if the owner of that computer is responsible for letting you do so. In either case, the author has provided full access to the sourcecode for your auditing, and it's your own fault you didn't use that to avoid the problem.
Feel free to come crying to the author with your problem, so long as you accept that it will be taken as entertainment, and not really as a serious complaint.

ESL also applies to itself. You may alter, redistribute and do whatever you wish with the licence, but try to keep in mind that multiple licences with the same name might get confusing, so at least try to pick an original name.