Yes. I don't really fit in at places where I don't have some kind of personal relationship with my co-workers. We don't stand in front of the whole office and make fun of each other, but when we're at lunch or in private we do play a little. Expecting people to robotically conform to an idealized notion of "professionalism" creates sterile workplaces. You spend enough time with someone and you will eventually become friends with them, co-worker or not.