From the online store:
Although the "im in ur" meme started off with virtual death and destruction (I'm in your base killing your d00dz), it was quickly overtaken by the legions of cute, fluffy, and irresistible. (And by that we mean cats.) Reclaim the phrase for the humans by captioning yourself. This shirt is full of write-on, wash-off goodness. Tell everyone you're in their noun verbing their noun! Bored with what you wrote this morning? Throw the shirt in the wash and think up a new saying. It's like Mad Libs meets Photoshop in a head-to-head deathmatch on your chest.
Imagine the possibilities! Visiting in-laws? We recommend, "im in ur offspring sproutin' ur family tree." Stuck at the office? May we suggest, "im in ur meeting eatin' ur donuts." Out for some wardriving? How about "im in ur unsecured network downloadin' ur pr0n." Techs could proudly wear their own "im in ur computer upgradin' ur RAM" shirts. Or for a more recursive bent, how about "im in ur lolbots crashin' ur server"?
If you have no idea what this shirt is referring to, congratulations, there may be hope for you yet.