I couldn't help but think of Vern when I stumbled upon 'Impov Everywhere' online.
For those of you who know Vern you'll know why. Look for the subway rides with no pants.

http://improveverywhere.com

I thought Frozen Grand Central was pretty cool. It was the first one I linked into.
Nothing controversial there.

Other than that I'm still not sure quite what to think.
The twist on this versus the common prank is that an objective is to make people happy not embarrass them to the point that they'd consider suicide.

The reason I post it is that it demonstrates an interesting look at actors and their audiences.
Caution: Only click on the links if you are willing to waste some time.