Surprise Appearances

Alright, I've been around the web searching for "Surprise Appearances" like a fat guy searches for a dinner plate at a family gathering. I have come up with Wrestling Surprise Appearances (pssh), Movie "Surprise" Appearances (Pssh) and the occasional Talk Show Surprise Appearance (getting closer).

But I really don't consider many of those as actual surprises. What I am searching for are some real surprises, you know, like what Brad Pitt has been doing recently - just popping up at random movie theaters to promote World War Z. I ask this because I attempt to catch the auditions of America's Got Talent since I don't usually care for the rest of the show. I've always thought how incredible it would be for everyone there if some huge star just popped up when his/her song was being sung.

But AGT isn't all, the Queen has been making random appearances over the years (I do believe she just popped up at a Live News Conference one time) and I know the occasional celebrity appearance makes headlines. Anybody know of some good ones? What can I say, when it isn't on the Chess Board, I do enjoy a good surprise.