Maybe TDD just isn't for him/her/other?

I prototype, then tests, then refactor and I know some people would be zealously against this style; demanding tests before everything. However my mind just doesn't work this way, I need to play with code to get ideas out of my head; coming up with relevant test cases takes a magnitude of time longer than making the prototype.

Now if your co-worker is not writing tests at all, this is a different matter, but as long as the code he writes is covered by a test suite in the end, what does it matter which order he/she does it in?