It is hard for me to understand from what you have written whether what you did is really bad, just a little inconsiderate or just something you had to do to get your work done.
If this guy has done this sort of thing in the past then they will know it and take that into consideration. I have been a supervisor and always hated to have to deal with these petty problems that could easily have been worked out by the parties involved.
My suggestion is to email your co-worker apologizing for any misunderstanding and explaining why you did what you did, and send a copy to the supervisor(s). Be the one who is open minded and open to comprimise. You want your bosses to know that you are part of the solution and will bend over backwards to avoid problems in the future. Of course if you are just pissed off and don't care about the job that much then you could always take a hard line position and rant like crazy.
