I like to play games in WoW. Like, children's games. It's rare I get someone else to join me, but when I do, I've yet to find a person that didn't have a blast.
Two simple games:
1) Hide and Seek - have to set some ground rules for this and people are on the honor system. One person stands somewhere and waits while the other player(s) hide. The hiders can not use stealth, forms, or anything else that is not available to all characters innately. The seeker can not use tracking or the /tar command. You have to restrict the area to some place small, which you define by the name that appears on your minimap...so if you're playing in Auberdine, as soon as the map changes to "Darkshore", you're out of bounds. After a few rounds, it's amazing the sort of hiding places people can come up. Night Elf architecture seems to be great for this kind of thing.
2) Tag - get a leather ball or some other throwable item. Whoever has the ball is It. They have to throw the ball to someone else playing. You'd be surprised at how tricky this can be when you play in dynamics like the range of the throw and line of sight. Tagbacks are frequent, so you have to plan how you throw for it. Because I have the paper airplane maker from the card game, I have an easy source for the objects for this game, and the paper airplane's slow path and minimum range add new levels to this. The places where this works best are wide open area that have lots of smaller obstacles. I played this for about 3 hours one day with somebody in Exodar.