I joke with my friends. I know their sense of humor. They know mine. Maybe I understand my team's sense of humor. I doubt it. I wouldn't count most of my co-workers among my friends. You also don't always know at who's expense or how expensive a joke may come, whether this is about football teams, geographic areas, hair (or lack thereof), etc. You also don't know if you tell a joke in an email in line with work related stuff whether or not that email gets forwards a bunch of times, might eventually find its way to someone you don't know who doesn't get the joke.

One of my biggest rules of humor is to know your audience. It's easy to know your audience in a comedy club or at a dinner table surrounded by friends. In most cases, you don't know your audience at work.