Yes it's a difficult one and of course you don't want your trusted friend and co-worker to get into trouble.

Are you able to confide in anyone else, another co-worker or manager perhaps?  You shouldn't have to put up with this.  Anyone who gossips has little else to do and as you say, obviously doesn't like themselves very much.

People tend to avoid a bully, keep their head down but this only allows them to carry on with their silly games.  If you can ignore it, but if things get worse I would speak with your bullying and harrassment officer or HR.

Your trusted friend and co-worker should do you a favour and put an end to this also.