Which language would annoy a PHP user?

We have nobody who coordinates the programmers at the company. Everybody uses the technology he wants.

Which programming language would you suggest to learn that would annoy a PHP user (who knows a bit of Java) and give him a bad time if he has to take over a project?

>>19
PHP was constructed by real computer scientists.

GHC performs type erasure. You can't have security and type erasure at the same time.