Well, you made it through March. The random weather hardships coming with the advent of spring social obligations. Life in general gearing up. And then some wag in your friends or family attempt to pull a con on you for their own amusement. "April fools!" comes the post-action battle cry.
As the tradition can be seen going back as far as the 1500s, it is without a doubt that some awful pranksters were pulling their shams in Sherlock Holmes's day. But we never see Sherlock Holmes celebrating the day by pulling one on Watson. Yes, he did wake him up at 7:15 one morning in early April to say "Mrs. Hudson has been knocked up," but that's more of a trick on our modern ear for words.
If you think about it, though, Sherlock Holmes was the perfect person to be playing pranks. He is a trickster throughout his career, fooling people with disguises, making cryptic references to what he knows and they don't, running fake ads in the newspaper to lure people to 221B. But he only ever runs his pranks on people with a purpose.
One trend you always notice in modern April Fool's Day behavior is the abuse of power differentials. Adults play pranks on children. Trusted sources use their podium to toss out some far-fetched story. And those desperate for attention offer a hoped-for bit of news to those desperate for that news. One of the earliest historical mentions of an April prank is a guy who would send his servants on silly errands, so it would seem like this April abuse of power has always been a part of it.
Ha-ha, foolish you for not being me, who has now shown myself to be up on you!
Sherlock Holmes didn't need April Fool's Day, because, in a very real sense, every day was full of fools for him. People came to him for help because they knew they were out of their depth -- many of them self-admitted fools. Early in his career, Holmes liked to call Lestrade and Scotland Yard fools. But Sherlock Holmes berated himself for being a fool many times as well.
If anyone wanted to take advantage of a power differential and just play prank after prank on people, Sherlock Holmes and his brother Mycroft would have been the pair to do it. But they didn't. Because they were smart enough to see the larger prank: That the smarter you are, you more realize that you don't know. (And at some point have to decide what lumber to put in your brain-attic and what to stor in your library, as Holmes pointed out.)
April Fool's Day would probably be best celebrated like Saint Patrick's Day, where everyone claims to be Irish. On April first, we all just admit what fools we are and go with it. For this one day, we quit bagging on sweet, lovable Nigel Bruce for being the dumbest Watson ever and chant "ONE OF US! ONE OF US!" Because, really, we're all ol' Nigel at some point. (And, if we're nice enough the rest of the time, people will still love us as Rathbone's Holmes did the old duffer.)
It's a day for silliness, and if we allow that we ourselves are most foolish of all, as Sherlock Holmes did on occasion ("I think, Watson, that you are standing in the presence of one of the most absolute fools in Europe."), I think we're going to have a much better time of it.
Now excuse me while I go prepare for some extreme foolishness.