Calling Your Bathroom Breaks

Everybody does it, but due to courtesy most people exercise discretion, merely saying something like, "Please excuse me for a moment." Not this character. When they have to go, they announce it loud and clear for everyone to hear: "I have to pee!"

Obviously, if a young child does this they might just not know any better; this kind of behavior is often associated with children during (or just over) toilet training who may need help with the process and are generally praised for doing so. If a grown character still acts this way, it can indicate childishness.

In a non-childish character, it can still be used to indicate boorishness. Like some other forms of impropriety, this can also be used to show that characters are comfortable dispensing with formalities between themselves. Or it could just be they've been holding it in so long that they don't have the mental energy to spare on being polite.

Sometimes a character who engages in this is faking in order to attempt a Bathroom Break Out.

Lastly, this can be played for a very mild form of Toilet Humor, sometimes as a Bottom of the Barrel Joke.

Examples of Calling Your Bathroom Breaks include:

Film

In Forrest Gump, both the book and the movie, this is used to indicate Forrest's lack of intelligence and social understanding. Most famously, he does this when he meets the President of the United States.
In Pulp Fiction, Vincent always crudely announces his need to go, which helps to differentiate him from his more professional counterpart, Jules. It also creates some incongruity with his character, being a professional hitman in a suit and tie.
In Murder By Death Sam Diamond does this twice, establishing his rudeness.

Diamond: I'm going down the hall to find the can. I talk so much sometimes, I forget to go.
Diamond: Shut up, all of youse! Nobody move! Stay where you are! [snip] I have to go to the can again. I don't want to miss nothing.

The Merovingian in The Matrix Reloaded, in perhaps the greatest example of his Sophisticated As Hell characterization.

Persephone: Where are you going?
Merovingian: Please, ma cherie, I have told you. We are all victims of causality. I drank too much wine, I must take a piss.

In the film of Scott Pilgrim vs. the World, Scott does this a few times to show how socially inept he is. A fantastic example occurs when he is caught in an awkward situation, asked about a girl he'd rather not talk about by his current girlfriend: a cut-away shows a wheel of excuses on the inside of his head which spins around and gets caught between "Who, her?" and "I have to pee." Scott's muddled response? "I have to pee on her."
In a deleted scene from The Enforcer, Harry is drinking beer with Kate, which ends with her drunkenly declaring that she has to pee.

Literature

In the Circle of Magic series, in the second book, when the four children are discussing what to do about the pirate attack, Tris announces loudly that she has to use the privy and leaves. Turns out she really was just trying to get away from the others so she could deal with it on her own.

Live-Action TV

On How I Met Your Mother Lily does this a few times over the course of the series, usually to indicate how working with kindergarteners for years has blunted her social sensibilities.
Taxi: In the first episode Latka tries to get Alex to help him with his English lessons, while Alex is on the phone.

Alex:Why don't you look at the phrases I wrote in the back [of Latka's english phrasebook]? "Get off my back." "Give me a minute while I go to the can." Study those.
Later when everyone is heading out to ride with Alex to visit his daughter in Florida before she gets on an airplane for France, Latka uses the "can" line on Louie.

Played with by Sheldon in The Big Bang Theory—Sheldon insists on a bathroom schedule and regulates the time at which meals are eaten in order to control when he and Leonard go to the bathroom, and several episodes concern him discussing this schedule with others. This illustrates both his rigorous need for structure and his totally inept social skills. Played straight by Leonard's mother who will stand and say "I have to urinate" before going to the bathroom.
In Friends episode "The One After The Superbowl Part 2", Chandler's date (played by Julia Roberts) invites him to join her in the restroom for some fun. He stands up from the table and proudly announces "I'm going to the bathroom now".
Barney Miller: In the toilet humor category, Fish has to go to the bathroom frequently. It's part of his aging process. Sometimes he announces it and sometimes he just implies it; it's a Running Gag.

Manga and Anime

Tamayo Kizaki on Angelic Layer does this earlier in the series in order to indicate that she is still childish. She stops after a particularly heart-wrenching moment of Character Development later in the series when she and Kotaro decide that they need to grow up. It doesn't help that this moment involves the two of them being trapped on an elevator for several hours, and all that implies...

Stand-Up Comedy

Discussed by George Carlin, who says in one of his routines how embarassing it would be for your fiancee to do this at a dinner party, then notes there is no subtle and tasteful way to announce this sort of thing publically and he personally has no interest in people who feel the need to discuss it with him.

Video Games

Yosuke of Persona 4 does this frequently, often at inappropriate moments. Parodied here.^{[dead link]}
In Marvel vs. Capcom 3 Deadpool's tag out quote is "Bathroom break!" This being Deadpool, there's no way to know whether he's serious or not.

Webcomics

In Questionable Content #1467, Dora is apologizing at length to Faye while they are in line for the ladies' room together. Faye cuts her off mid-speech this way when she reaches the front of the line.

Web Original

Trollvorlord from Bronyism occasionally does this, along with calling out trips to Burger King and video games breaks.

Western Animation

Veggie Tales: At the very end of the movie "Lyle the Kindly Viking," Larry, the consummate manchild, sings "I have to go to the baaathroooom," much to Bob's chagrin.
In the first episode of Avatar: The Last Airbender Sokka is attempting to "train" very young children to defend their hometown, since all of the men are away at war. He is constantly interrupted by their need for a bathroom break. This shows how futile Sokka's task is, as he is clearly dealing with children who are only three or four years old, as well as illustrating how well and truly defenseless they are should the Fire Nation army come a-knocking...