Watch: I choose to ignore the warranty clause per clause 0. Also, since that clause exists, I can choose to apply it to other code I combine it with (unlikely, but its a dumb license that way)
Past that, I'm not convinced that due to clause 0 that it can be combined with other code, and I am of the opinion that more licenses are not good for open source development in general.
A responsible coder, given the desire in the wtfpl, would adopt a richard hipp style posture, or choose mit,bsd or apache.
The WTFPL is an all-purpose license and does not cover only computer programs; it can be used for artwork, documentation and so on. As such, it only covers copying, distribution and modification. If you want to add a no warranty clause for a program, you may use the following wording in your source code:
How does this make life harder for hackers? Explicit permission is given to do whatever the fuck [you] want to, which includes hacking.