[bontoJR]

It's a nontrivial task, I wouldn't waste too much time in trying to prove that someone's code is complex. I tried in the past with the result of being appointed as "lazy" or "basic" developer. I heard arguments like: "if you think this is complex then you are not so good" or other very unnecessary arguments.

Don't prove he's writing complex code, it would be interpreted as "being wrong", but instead prove that you can come up with easier and cleaner solution. Write your own, test it and then propose it to the original author, see if he can admit that your solution is cleaner, easier to understand and easier to handle. I did this few times with very good results on feedbacks.

[DamnYuppie]

This is the path that I eventually started to take as I progressed as a developer. Most people when shown a better way are open to it as long as it isn't presented in a manner meant to convey superiority.

[bontoJR]

Yes.

...and one thing that can also happen is, when discussing a secondary solution, a third one can come up that is even better.