Whenever I game, it's impossible for me to start on time. Everybody's usually here roughly on time, everybody's sitting around the table with their characters made, dice ready, superfluous sheets of paper ready, something to drink, and everybody looks at me (or, alternately, nobody at all is paying attention to me.)
My next step: Hey guys, we're taking 5.
I always need an extra five minutes where I'm not helping somebody with rules or drawing out dungeon levels or whatever to refresh my brain juices and let the world sink in. It lets me introspect on how I'm feeling and any cool ideas I want to make sure to use today. It lets me get a gauge of my players, how they're feeling, the general mood of the group, and how to make that work. Nothing's worse than running a silly game when your group is feeling serious, or a serious game when your group can't stop making penis jokes.
And then when we're done stuffing our faces or watching TV or using the bathroom, everybody sits down and all eyes are on me. (Eventually.)
It's my own pre-game ritual, if such a thing exists. We can't all gather up and say "hey man how's it going" and eat food and all of that and then start as soon of us are all sitting down. There has to be that break in between, because otherwise there's seriously no way I'm going to DM.
No idea why that is, but that's just the way it has to be. It might be the only thing in the world I'm anal-retentive about- luckily, it's something that nobody really minds and besides, I am the DM 99% of the time. What's the matter with having a harmless quirk, anyways?