I also have that train of thought that the hosts should make the first move. After all, it is their house. What's interesting is they all know why they've gathered in that same room, yet, everyone stands there like they're at a junior high dance afraid to move.
The last house party we went to, we played strip pool as well. It didn't take long before the fun began. Probably less than 1 minute after the first shirt came off. All started by the host, of course.