Thanks for all your answers! It really helps me to deall with a situation like this. My first thought was also the bolt cutter / super glue / chain and padlock solution, but this would mean that I woud do something thta I don't want other people to do to me so this would not be right. I will have a chat with him and try to stay calm and polite (although I know that it will not be easy for me). Again, many thanks. I started thinking that I was overreacting, but most of you seem to agree.