The crowbar can be found in the girl's bathroom in the red tool box. If you take the crowbar all the way over to the far left of the map where the Sewer grate is you can use it to open the grate. Swing the crowbar to open it and it will stay open unless you reset your entire game file.
As a weapon the crowbar will afflict damage upon hitting another character with no knock back damage. Take two hits to kill a friend.