[rebane2001]

> If that were the case, why don’t we have several of these prank days per year? Maybe monthly?

If New Year's is so great, why don't we celebrate it twice a year? If Christmas is so good, why doesn't Santa bring gifts every month?

> It’s because on a scale of 0-10 these pranks usually rate somewhere between 0 to 2 in terms of humor and > 2 in terms of annoyance.

For your example, yes But a lot of the "pranks" aren't really pranks per se but more of just having fun and expressing creativity If you look at what Google does each year, they've always had fun and creative ideas, that don't fool or annoy anyone and are enjoyable (with a few exceptions)