When it comes to knock-knock jokes, it helps to be 5 years old: You can slap your head, roll your eyes, and run outside and play.
In a courtroom where the defendant is charged with second-degree murder, a knock-knock joke has all the appeal of a bar of soap on the shower floor.
It is difficult to imagine how Don West, defense attorney in the trial of George Zimmerman, the man accused of killing 17-year-old Trayvon Martin, worked through the thought process that led him to slap his own forehead and say to himself:
“Yes! A knock-knock joke is just the way to begin my argument. No, wait, wait! Even better and ridicule the people who will decide the fate of my client! ‘Colbert Report,’ here I come!”
Thus, when Zimmerman’s trial began Monday — in a courtroom where the parents of the victim were present — he offered a little joke:
Knock-knock. Who’s there? George Zimmerman. George Zimmerman who? All right. Good. You’re on the jury.”
No one cued the laugh track. Lightning is funnier.
West’s opening-day thud may have seemed amusing over coffee in his own kitchen, but even he knew it was inappropriate. We know because he said so in a lengthy, disclaiming preamble that would have killed even a funny joke. Before launching into The Joke, he warned jurors that they might not think it’s funny under the circumstances. He even asked forgiveness in advance just in case they found the joke inappropriate (his word) and to hold it against him, not his client.
At this point in a comedy club, never mind a courtroom, anyone listening would be squirming in vicarious embarrassment for what was to come and was surely going to be a very bad/unfunny/inappropriate joke. Why tell it?

Because everyone is a comedian these days. Or at least everyone wants to be. Comedy, rather than providing relief from our too-serious times, has become the currency of choice. Indeed, as more and more people turn to “Comedy Central” for news, comedians have become among the most influential arbiters of current events.
Not, as funnyman Dave Barry would say, that there’s anything wrong with that.
Ever since Jon Stewart told CNN’s “Crossfire” hosts in 2004 that their left-right political slugfest was bad for America (and then-CNN president Jon Klein soon after killed the show), the power of the comedian has surged past the serious commentators.
Who wants to be the straight man when the funny guys get all the girls?
Not that comedy isn’t commentary. But time and place are as important as the punch line. When a comedian is funny, we never forget that he is primarily a comedian. When a defense attorney plays a comedian at a murder trial, our sense of verisimilitude is thrown off kilter. Wrong character, wrong scene, wrong everything — especially the audience, which included the parents of the victim and the people whose sympathies West was trying to enjoin.

After much criticism, West sort of apologized for his lapse in judgment. He was sorry if anyone was offended, but he still thought it was funny.
Humor has a role in public life, obviously, and comedians make valuable contributions to our understanding by casting a light on our hypocrisies and self-righteousness. Nothing quite delivers a memento mori like a well-placed barb. But that barb best be sharp, and it better be well-placed. West’s joke fell flat because it was neither.
The only imaginable use for humor in a murder trial — and this is a stretch — would be spontaneous and self-deprecating, which rarely goes wrong. Insulting one’s potential allies, on the other hand, is an unforced error of conceivably catastrophic consequence. It’s bad enough to be the butt of a joke, but a joke that’s not funny?
The poor jurors in Zimmerman’s trial were told more or less that they’re so uninformed that they just might be stupid enough to buy the rest of his defense. Let’s hope West has better material in his briefcase or Zimmerman, should he be convicted, may have unique grounds for appeal: His lawyer couldn’t tell a joke.

Email: kathleenparker@washpost.com.