(YouTube link)
What do you take with you to a Little League game? If you’re Improv Everywhere, you take a cheering section, a Jumbotron, some play-by-play announcers, and a blimp. It sent a bunch of unsuspecting ten-year-old players (and their parents) to baseball heaven. Read the particulars at Improv Everywhere. Link -via Metafilter
They're not entertaining everyone else as much as they are entertaining themselves. To do so, they (the organizers at least) take a view that their prank will obviously be fun for everyone. If you are a target and you don't have fun, then you didn't get the joke or you're just boring.
If the kids enjoyed it, then great, I'm glad for them. But this doesn't make IE's pranks smart, funny, or entertaining if you're the target.