They Might Be Giants (film)

A 1971 film starring George C. Scott and Joanne Woodward. Adapted from a stageplay. The main character believes he is Sherlock Holmes after the death of his wife leaves him with severe paranoia. Dr. Mildred Watson is an analyst caught up in the man's brother's scheme to control his money through having him committed, while at the same time the brother is being pursued by a shadowy blackmailer in sunglasses. The film presents many fun elements, from spoofing/recreating classic Sherlock Holmes tropes, to pondering the popular themes of insanity vs society's consensus reality. Scott and Woodward give magnificent performances, though the script tends to drift into stagey pretentiousness near the end.

Oh, and yes, the band named themselves after this story.

Tropes used in They Might Be Giants (film) include:

Aw, Look -- They Really Do Love Each Other: Initially, however, they are very antagonistic towards each other, he annoyed and fed up with her attempts to 'cure' him and her exasperated by his maniacal antics.
Clap Your Hands If You Believe: The story plays with the idea of how groups of individuals who have chosen to embrace a delusional reality can create their own consensus reality which just might, depending on how you interpret the ending, become real.
Completely Missing the Point: While it's actually a rather sad note of the film because his insanity as just driven what could have been his only chance at finding love away, Justin/Holmes angrily shouts into the dark as if he has nothing left to lose,

"Moriarty, strike me now!"
But when met with nothing but silence he grins and says with self-satisfaction, "You see? He's afraid of me! He knows what I can do."

Crazy Awesome: Justin/Holmes has moments like this--such as using his Sherlock costume cane to deftly beat some asylum goons or using a bizarre form of schizophrenic Hyper Awareness to become the target of an actual plot going on in the background, utilizing clues that make little actual sense and are probably not even related.
Detective Drama: Something of a subversion, since the main character thinks he's Holmes, but all the deductions he makes are patently ridiculous (even if the story allows them to be true), the clues he constantly searches for are more like the manias of a schizophrenic, finding meaning and messages in completely unconnected and unintentional words, and he commits the cardinal sin of theorizing without data (he posits the existence of Moriarty without any evidence). However, the presence of the plotting brother and the shadowy blackmailer turns this into an interesting, if off-kilter, example.
Did Not Do the Research: Doctor Watson's use of the term "paranoia" when referring to specific aspects of Justin/Holmes' behavior is woefully inaccurate from a clinically psychological perspective.
Everyone Calls Him "Barkeep": Most of the people close to him call him Justin Playfair and he himself admits that "scarcely anyone" calls him Holmes, but yet most of the city crazies seem to know him as Sherlock Holmes.
Funny Schizophrenia: Well if you don't believe that Justin is actually right, his crazy antics come off this way, such as suspiciously observing pigeons with a magnifying glass.
Hey, It's That Guy!: Aside from the obvious Mr. Scrooge playing Justin, Grandpa from The Munsters makes an appearance in the film.
Intimate Psychotherapy: The Doctor assigned to "cure" him of his alleged monomania later falls in love with him and embraces his delusions, taking on the persona of Watson.
Mind Screw: The ending is quite a headscratcher, as you are left wondering, 'what just happened?' Did the pair actually see Moriarty? Did they get run over by a car, smiling wide-eyed all the while? Or was that the spotlight of the police?
Milkman Conspiracy: Justin/Holmes points to such disparate incidents in the newspapers as people dying from crossing the street, grandmas being raped and beaten, and excursion boats exploding as evidence of Moriarty's near omnipresent nefarious influence.
"No" Means "Yes":

Justin/Holmes: "Did you enjoy your first detective work?"
Watson: "No."
Justin/Holmes: "Come on, I know girls--no means yes."

Xanatos Roulette: Moriarty must be the master of this if Justin is correct about how extensive Moriarty's shadow empire is.
Ragtag Bunch of Misfits: The epic march near the end gathers together all of the city crazies as well as most of the people they've helped throughout the film, all marching in tandem alongside Justin/Holmes and Watson. Played for Laughs when he asks them, "Anyone who knows why we are here raise your hand." No one does.
Title Drop: Justin's speech in the taxi about why the Don Quixote spirit helped carry forward history and progress, by looking at things and thinking of what they might be--for example windmills because...They might be giants.
The Moriarty Effect: As a Sherlock film, this is predictable enough