Yeah, I would pick a real license and make it clear what it is, otherwise many people would be reluctant to use that code.
FWIW, the FSF does not recommend wtfpl:
WTFPL, Version 2 (#WTFPL)
This is lax permissive non-copyleft free software license, compatible with the GNU GPL.
We do not recommend this license. If you want a lax permissive license for a small program, we recommend the X11 license. A larger program usually ought to be copyleft; but if you are set on using a lax permissive license for one, we recommend the Apache 2.0 license since it protects users from patent treachery.
See:
https://gnu.org/licenses/license-list.html