Inconvenient Itch

When a character suddenly becomes afflicted by an intense itch, and they either can't scratch it for fear of certain consequences, or have no means of scratching it on their own. The intensity of the itch will often scale upwards with their inability to take care of it, especially if they are tied up or busy holding a sensitive package full of Explodium.

Nearly always Played for Laughs, the victim of an Inconvenient Itch will often be left begging for their companions (or even antagonists) to help them out. If the afflicted character is left tied up and alone, the humor of the situation may arise from their attempts at contorting their body in an effort to find relief. Though the Inconvenient Itch can hit any part of the body, the nose is a popular target.

A subtrope of Rule of Funny. Compare Amusing Injuries, Potty Emergency, and Anti-Sneeze Finger. This trope is a typical result of being Bound and Gagged in comedic works.

Examples of Inconvenient Itch include:

Film

Undead or Alive: Luke's nose starts to itch when he and Elmer are stripped naked and forced to ride on a horse together with their hands bound. Once they are finally untied, Luke spends several moments flailing about with his now-numb hands trying to scratch it.
When he first starts working out, Dennis in Run Fatboy Run gets a nasty, itchy rash in his crotch that he absolutely has to scratch... as he is at work as a security guard in a lingerie shop. One can guess what this looks like.
Shrek in Shrek the Third is trussed up in some Impossibly Tacky Clothes for a royal appearance, and suddenly develops a horrible itch on his rear. He has some poor servant scratching that itch when the curtains open, giving the waiting crowd a view they really didn't want.
Cheech and Chong use this in Nice Dreams. Scene opens with Cheech screaming his lungs out and writhing, clearly in a straitjacket and prison cell. Maybe all those psychelics he took finally fried his brains? Finally he manages to get his wits together to enunciate the problem. MY BALLS ITCH! Enter Chong.
In The Adventures of Baron Munchausen, the king of the Moon (Robin Williams) is gleefully happy to be rid of his lower body, leaving his head to roam freely in intellectual pursuits. Then he begins feeling a terrible itch in his non-existent body, and is completely unable to do anything about it.

Literature

The Adventures of Tom Sawyer: This happens to Tom Sawyer when he is trying to hide silently in the dark.
Robert Heinlein's Have Space Suit Will Travel. While trekking across the lunar surface, Kip itches all over but can't scratch because of the space suit he's wearing.
Starship Troopers also addresses this as the only major fault in Mobile Infantry power armor.

Live-Action TV

On How I Met Your Mother, Marshall realizes he has head-lice halfway through a job interview, and starts "discreetly" trying to scratch it. Eventually, it's too much for him and he screams out "I HAVE LICE!". Suffice to say, he did not get the job.
On an episode of Sabrina the Teenage Witch, two men must face a magical test to win Sabrina's heart, which involves running through an obstacle course to reach Sabrina, who is sinking into a pit of quicksand. At a point where her hands are submerged, seemingly pinning her arms to her sides, Sabrina says: "Help, someone save me! Or scratch my nose..."
In one episode of Mash, Margaret is afflicted by a rash on her backside but can't scratch because she doesn't want anyone to learn of her plight.

Newspaper Comics

One Calvin and Hobbes Sunday strip has Calvin trying desperately not to scratch his mosquito bites, because he knows that scratching will just make it feel worse later. Calvin's pain is visualized by showing Calvin being eaten alive by ants, or with his head on fire.

Theatre

In Fiddler on the Roof, there is a scene where one character invokes this:

"May he get an itch he cannot scratch!"

Western Animation

In one Danny Phantom episode, Danny and Valerie end up in the Ghost Zone and are forced to team up against Skulker. After a while, they end up trapping him, tying him up, and leaving him on the floor as they exit the zone. At that point Skulker exclaims: "Err...Guys, there is a problem... my nose is itching."
In the Wartime Cartoon "Donald Gets Drafted", Donald Duck is instructed by Sergeant Pete to stand still. Unfortunately, he's standing on an anthill.
In the Looney Tunes short "An Itch In Time", Elmer's dog tries very hard not to scratch a flea bite lest he get the ultimate penalty: a bath!
On Dexter's Laboratory, Dexter gets the chicken pox and is told not to scratch the pox, or he'll turn into a chicken. He tries ways of keeping from scratching, even restraining himself completely, but nothing works and he eventually goes on a scratching spree... after which he indeed turns into a chicken.

Real Life

The worst timing for a case of Inconvenient Itch.
It is often said that the spots which are the hallmark of chicken pox will just itch even more if you scratch them.
A burning itch may be a symptom of peripheral neuropathology caused by diabetes. It may appear at inconvenient times, and scratching doesn't help.
Any skin or nerve condition that causes long-lasting itches; eczema, bug bites, chickenpox, hives, the aforementioned side effect of diabetes, whatever. Scratching will only relieve the itching temporarily at best, and if you keep scratching it'll destroy your skin, so you really shouldn't scratch it at all.
An Irish-Gaelic curse runs, "May you be afflicted with the itch and have no nails to scratch."
Truth in Television for anyone who gets an itch in an awkward place while they're in public.
- God help you if you get one in the middle of a parade and you're in the marching contingent.