I'm not knocking it! It looks fun actually, I'd totally do it too. We all need something to fidget with. I'm kinda jealous.
Most guys say that if they were women, they'd be playing with their own boobs a lot. Boobs are soft and squishy and most everyone I talk to likes them. They are fun to feel. But it is not socially acceptable to play with your boobs in a staff meeting.
When we're pregnant we get to rub our bellies and that's fun, at least for a few months. It's big and round and firm and sometimes it moves. It's just cool to feel and its ours, all ours. But then the baby's born and we go back to being normal people with nothing really interesting going on.