Picking their noses i suppose. I come often in big offices, and most of the time it seems like the majority is bored. They definitely don't drown in work, that's for sure. One time i walked into someone's office, and he noticed too late that i entered, so he was too late using his browser's backbutton, hiding the pornsite he was checking out.
Sometimes you hear them complain about how hard they had to work the other day, and i can't help laughing about that.