Office etiquette - Coworkers overstay their welcome in your office/won't leave

How do you handle this?

I have a coworker whose office is starting to become the "water cooler" spot, so to speak. He's in the office next door to mine, and we have a couple guys in the office who are seem like they're literally in there every 30 minutes or so. It's gotten a LOT worse this week, and I realize that it's partly due to it being Christmas and them being bored/antsy to get out of here. But how should he handle it?

What I do when someone comes into my office just to chat when I don't want to (about non-work-related shite) is sort of sit there focused on my computer (usually email or TD) and don't really ever look away at them. And of course I converse with them for a minute (it's not like I completely ignore that they're talking), but that usually gets the point across enough for them to leave or wrap it up. And I'm never mean or an a-hole about it, and of course sometimes I do chat with them anyway.

My buddy next door to me though (who may or may not post here), he's a lot nicer (for lack of a better term) and so he's sort of "created these monsters" that now come to visit him about ten times a day (and almost always overstay their welcome). I've tried calling his office phone and he'll play it off like it's a work call, and that has worked, but is starting to work less and less. It aggravates him, but it's fricking hilarious to me, and I try to walk by and make faces at him or give him thumbs up as much as possible to frick with him.

So what are ways to get them to a) maybe not stay as long all the time, and b) maybe get them to visit a little less.