Tinkle in the Eye

I still don't like changing diapers, but ever since Hammie came along my reflexes have really improved.

—Daryl MacPherson, Baby Blues

Any time Hilarity Ensues because someone without experience is taking care of a baby, you can expect the writers to bring out the horrible and dreaded act of The Diaper Change for quick and easy Toilet Humour. This is frequently taken one step further when the child in question is a boy, since the infant will frequently "open fire" on his caretaker mid-way through.

A Truth in Television trope, as anyone with any significant experience in caring for babies will confirm. Hardly exclusive to boys in real life, but in fiction it's only ever really brought up with them since they're the only ones for whom it's a potential projectile.

See Urine Trouble, which covers incidents involving animals.

Examples of Tinkle in the Eye include:

Advertising

There was a horrifying commercial by Huggies, (what else) a diaper brand that showed a father taking his baby into a bedroom to change him. That baby "opens fire" all over the ceiling but the stream stops instantly when the diaper is closed.

Anime and Manga

An episode of Sailor Moon during the "Eiru and An" arc featured Darien caring for a baby. An got this when she tried changing the baby's diaper.
Koharu Biyori: Yui of this ecchi series has this happen to her while babysitting. Worse, the accident causes a short in the Robot Girl's system that deletes all the baby care information she had downloaded specifically for the task.
Akkan Baby : When Shigeru and Yuki find themselves looking after an abandoned infant, they inadvertently give him this opportunity,

Film

In Three Men And A Baby. (Although it was with a baby girl in this case.) Don't use your expensive leather couch as a place to change diapers.
In Riding in Cars With Boys the main character gets it right in the mouth as she struggles to care for her newborn son. As she rants and raves and brushes her teeth her mother laughs and goes to finish the change for her.
At the beginning of Kung Pow! Enter the Fist, the Chosen One pees in ~~Master Pain's~~ Betty's face as a baby, in self defense.
Son of the Mask The baby has so much urine it seems like he's doing it on purpose. And since he has special powers, being the son of the mask, he probably is.
In a variant, Lily Tomlin in The Incredible Shrinking Woman was nearly drowned in an unfortunate close encounter with a "Betsy Wetsy" doll.
In the middle of The Three Stooges movie, when the Stooges disguise themselves as nurses in order to kill a man, the Stooges are forced to change a bunch of diapers inside of a nursery, ultimately turning this trope into a slight subverted (and rather disturbing) variation of their infamous Pie in the Face gag.

Live Action TV

The Nanny: Fran is changing a baby boy's diaper when Max warns her to stand over to the side rather than in front in case of this trope, commenting that his own son was able to hit the wall clock.
Subverted in Dinosaurs. It appears that Baby Sinclair is doing this to Earl, but he's actually shooting him with a water pistol.
A favorite theme on America's Funniest Home Videos.
Chouriki Sentai Ohranger: Juri ends up on the receiving end of this in an early episode.
Tokusou Sentai Dekaranger: Umeko witnesses a regular mother going through this and laughing it off, teaching her an important lesson in motherhood (she's currently babysitting a baby alien twice her size).
Juken Sentai Gekiranger: Ran winds up babysitting both her teammates when they are de-aged to a kid and a baby—one of them pees into her face, and gets teased about it well after he's back to normal.
In an episode of Diagnosis: Murder they change a baby's diaper. The pixie faced doctor comments on how babies whizz in peoples' faces when people change their diapers on TV. He then changes the baby's diaper and gets whizzed on.
The Lone Gunmen find themselves caring for a baby, and none of the three have a clue about baby care, with the predictable result during a diaper change.
Good Luck Charlie: Baby girl Charlie is mixed up with a baby boy. The kids babysitting her manage to switch her back, but are ultimately busted when none of them can explain the pee stains in the living room.
This happens in one Charmed episode. Piper freezes time to dodge the stream.
This happens in the Smallville episode "Ageless". Clark Kent dodges the stream.

Newspaper Comics

A strip of Baby Blues featured dad Daryl dodging, weaving, and ducking the first three panels, before finally saying the page quote to his wife Wanda as he holds his son.

Web Comics

Happens to Rayne in this Least I Could Do strip. He does it himself in this one.

Western Animation

Subverted in the Fairly Oddparents movie "Fairly Odd-Baby", where after the baby's gender is speculated over the entire series, Timmy realizes the baby is a boy when a stream of water shoots up between in the middle of a diaper change... "because boys love water guns!"
Family Guy: Stewie Griffin has done this on purpose more than once.