A lot of micro-holidays we've compiled Not every one of WOTLK Gold them but lots of them are designed with social interaction in the mind. There's also the Salute of the Guard Day that's a bit hiddenly social, however the method used to achieve this is that the number of enemies you've killed as guards is monitored. 

There are times when enemies will come after you as you've assumed the look as a guard during the holiday and when you're surrounded by hundreds of people who are guarding the throne within Stormwind and Orgrimmar's Gates of Orgrimmar, then there's bound to be more intruders and you'll all be absorbing one another's abilities as guards which is why you're glad to meet others playing.

Another approach to thinking about the social gathering is to consider one of the Spring Balloon Festival holiday where the way the celebration works is that people stand in line waiting for balloons to go off and fly off very quickly. Each balloon will leave with one NPC that talks to you, and there are three other players picked randomly. Not necessarily from the same gathering. 

You're given a view from Azeroth as well as Outland or wherever else you are, which is a nice thing in its own. Also, you're with some strangers, and the NPC could be able to say a few things that encourage you to engage in conversation with each other. The NPC might say "Here's an idea I thought of ha, ha, Ha. Anyone else have any great jokes?" After that, he'll remain silent for  buy WOTLK Classic Gold a while and perhaps people will begin talking.