I once worked in an office that would always end department-wide emails with a gif of a cute animal. It happened so often that it became an unofficial rule in our office. People would be upset and complain if a gif was left off an email.
One day I noticed that mammals were getting all the love so I attached a gif of a snail to try to mix things up.
People were furious with me and shortly thereafter people stopped sending animal gifs to each other and morale dropped. I guess the lesson here is never try mess around with the rules, and never, ever show a mollusk love.