Almost everyone I work with at my current job is a hard core Linux enthusiast and they code primarily in Perl. The project I'm working on is in Java and one of the Perl guys has been transitioned over to work with me. He usually tries to do everything in the way he is used to and finds more powerful. For example, he prefers to edit his files in Emacs and does a lot of stuff via Bash scripts. I have no problem with that and he is making an effort to use the tools I'm more used to so its easier for me to help him if things go wrong.
As a "Linux person" he uses grep a lot. I use it a fair amount when I need to through Cygwin, but no where near as much as he does. I can't call it a day without hassling one of my co-workers, so I've started making fun of his chronic grepping. Last night I decided he needed a shirt. Something catchy:

As a side node, CafePress now has black shirts. Oh what a glorious day!