Many players like to ask us if pranks are allowed, or causing trouble to another player "just for fun".
What you think is a "harmless prank" won't always be understood as such by your target. Things done "just for fun" aren't funny for everyone. Some will get angry, others will be scared about what's going on. Some also get worried about bugs and get in touch with the staff for help, only to realize later that nothing was seriously wrong.
That ends up causing trouble to the people being targeted and the staff which looks into potential problems. Taking items "for fun" is dangerously close to stealing and should be avoided, same as changing someone else's build.
Pranks aren't strictly forbidden, but think carefully about setting one up: your target might not like it as much as you think.
This information has been added to the rules page to ensure that everyone has a chance to be aware.