The Shortest Distance Between Reader and Character is a Punchline
Giving a specific character good punchlines offers immediate and invaluable access to their mind even when described in third person. Whether their style of humor is vitriolic, dry or just flat-out funny, listening to them while advancing or at least not detracting from the plot offers the reader unguarded moments into that character's world view and perhaps even a hint about their past.
To cite an example from one of my own books, I think perhaps the best punchline in Tatterdemalion came right after the protagonist Scott Carson has a public spat in front of the whole team with Buffalo Bill Cody. Carson, at first reluctant to go on Bill's grand adventure chasing Jack the Ripper, is chafing under the bit and is frustrated about being left in the dark. He calls Bill a fraud for presenting the Wild West in his show as it never really was. Cut to the quick, Cody stalks upstairs.
Carson immediately runs up to apologize to him but also to find out why he's doing his level-headed best to keep the much younger man from the center of the action. Bill relates a story in which his old Civil War colleague, Wild Bill Hickok, shot a man dead right in front of him when the gunfighter was three years younger than Carson (18). Bill then concludes by saying he doesn't wish for Scott to turn into a stone cold killer (which alone not only helps to define Bill's depth and mode of thinking but also is an adroit piece of foreshadowing considering the harrowing ending).
But to put a fillip to the exchange, Carson finally gets around to telling him, "I'm sorry I called you a fraud, Bill." Then he replies, "Apology accepted. And I'm sorry you're right."
It's an unguarded, organic moment that doesn't necessarily detract from the plot as much as it helps delineate Buffalo Bill's character even more. Not only does it display his often laconic wit, it also shows in this vulnerable moment that he's capable of self-effacement if approached the proper way.
In Lyndsay Faye's Timothy Wilde trilogy, the narrator and main protagonist, a charter member of the 1840's NYPD, has a mordant and trenchant sense of humor that's always aimed at his dissolute older brother and police superior Valentine and his old nemesis, the brothel madam Silky Marsh. In chapter two of the second book, Seven For a Secret, Wilde starts out by telling us,
I am that rarest of deviants in New York City: one who feels about politics the way most men feel about scraping pig dung off their boots. My antipathy stems from the fact that I spent most of my life thinking my brother, who is an enormous cog in the Democratic engine, one hundred per cent despicable. I'd been mistaken--- Val is only three quarters despicable.In 66 simple but beautifully-crafted words, Faye tells us with complete, ruthless honesty Timothy's loathing for the Tammany Democratic machine that brought the NYPD into existence, for politics in general as well as for his brother and why. She also gives us a bit of descriptive imagery as to what it was like to live in 1840s's Manhattan (pig shit on one's boots and nearly unanimous political engagement brilliantly synonymized in one simple simile).
Despite the trilogy's troubling failings, Timothy Wilde's humor is almost invariably something of a marvel. Much of the complex and often stormy relationship with his older brother stems from the fact that when they were both boys, Valentine accidentally set fire to the family home and killed their parents. Then in 1845, the bar Timothy worked in was burned down, leaving him scarred for life. This is a man that has lost much in his life. Yet in Faye's universe, he not only retains his sense of humor, he also perseveres and becomes the NYPD's first detective.
To cite another extremely worthy example of humor fleshing out a character, one could do much worse than look to Charlie Parker. Irish author John Connolly introduced Parker to us 15 years ago in one of the most spectacular debuts in recent commercial fiction with Every Dead Thing. The Parker series is a latter-day interpretation of the pulp fiction thrillers mastered by the likes of Raymond Chandler and Dashiell Hammett. Always told with a quasi-supernatural twist, if one were to imagine the wise-cracking Sam Spade in the woods of Maine or the streets of New Orleans, you'd begin to get a handle on Parker's psyche.
What makes Parker virtually unique in modern day crime/horror fiction, aside from the freakishly high quality of his barbs that rival anything by the best TV and movie scriptwriters, is the sheer stubbornness and enduring nature of his sense of humor. In Every Dead Thing, Charlie Parker's entire family is slaughtered by an ingenious serial killer named The Traveling Man. Early in this debut, Parker is seen years after his wife's and daughter's murder and he says this:
No one reasonably expects you or your characters to be Bob Hope or Rodney Dangerfield. But humor in your protagonist's psyche ought not be underestimated. Humor is something most readers appreciate and, if treated properly, can offer instant access to their minds whether you're writing about them in first or third person. As the canard goes, "Many a true word is spoken in jest." And we and our characters are never truer to our natures than when we're either scared or cracking wise.
Which is often simultaneous.