It's my favorite glitch, but made special by the sheer amount of stuff (furniture, players, NPCs) that did pop in, without a single wall or floor.
It was made even more special by the fact that we were even able to go up to the 2nd floor of the inn (courtesy of an invisible staircase whose location we remembered).
[Update: 14 June 2014]
So normally the “Go out the door and inside someone's head” glitch is a little on the macabre side, with teeth and the backs of eyeballs and such. But here the mashup of heads (I think there were at least 3 of us occupying the same space) made for some beautiful abstract art.