Grandpa: I watch the baby.
Marge: Where is the baby?
Grandpa: (genuinely surprised) You left me with a baby?!
A kid gets away with audacious stuff because they've been left in the care of a grandparent who is too senile and addled to notice if, say, they disappear through a Portal Picture to a Magical Land for a few days (probably because they're a victim of the Senior Sleep Cycle). Makes you wonder what in the world prompted their parents to leave them in said grandparent's care in the first place.
Compare Scatterbrained Senior for general senior senility traits.
- Big Fat Liar Kaylee agrees to go on an adventure to Hollywood with Jason even though she's supposed to be staying with her Grandma Pearl for the summer. How does she get away with that? By having big jock Brett visit Pearl in her stead. Even Kaylee is surprised it works.
Jason: That woman doesn't even know what year it is.
- Combined with Parental Abandonment in Bad Santa: The Kid's mother is dead, his dad is in jail and he's left with his incredibly senile grandmother.
- Grandpa in The Lost Boys turns the trope on its head; seeming clueless and, frankly, a bit weird, throughout the film, he eventually saves the day like he does it every day, handwaving the existence of vampires and completely stunning the other characters:
[Grandpa silently gets a root beer from the fridge.]
Lucy: Dad..? Dad, are you all right?
[Grandpa chugs at the root beer]
Grandpa One thing about living in Santa Carla I never could stomach: all the damn vampires.
- Vada's grandmother suffers badly from dementia in My Girl, so much so that it's Vada's job to babysit Grandma whenever a funeral is happening downstairs (Vada's father is the funeral director). It's a rare example of the obliviousness not being Played for Laughs, and in fact is a point of contention for Vada and her dad at one point when Grandma gets out of Vada's sight and starts singing "One More for the Road" into a rose in front of a roomful of mourners.
- Lina's grandmother has dementia, leaving Lina with little supervision when she goes off to save The City of Ember.
- On Everybody Loves Raymond, there's one Halloween night where Frank Barone, charged with dealing with trick-or-treaters, obligingly doles out Ray and Debra's novelty coloured contraceptives, thinking they're some sort of brightly coloured chew sweets.
- In an episode of iCarly, Carly can't stop Nevel from messing with her website because while his mom is on a cruise, the only person in charge of him is his grandmother, "and she's hopelessly confused." Subverted with Carly and Spencer's grandfather, who seems to be the sanest member of their family and actually shows up in one episode to take custody of Carly because of a perceived lack of responsibility from Spencer.
- In Scrubs, Elliot mentions that, for a couple of years in high school, she lived with an elderly couple who were friends with her parents and didn't have many rules because "I'm pretty sure they thought I was a ghost."
- The quest in Peter and the Wolf is done while Grandpa's asleep and oblivious to his grandson's disobedience.
- Max Tennyson of Ben 10 also subverts the trope. He knows full well what Ben is up to, and encourages Ben to be responsible about "going hero." Ben still gets away with audacious stuff, though, that would get a normal kid spanked or grounded. Or dissected.
- Humorously averted on Class of the Titans, where Herry's beloved Granny seems to be the only parental figure who knows what the kids are really doing. She even helps them take on Cronus in a couple of episodes.
- Timmy's Pappy on The Fairly OddParents subverts the trope. He cheerfully goes along when Timmy, Cosmo and Wanda drag him into an "old timey cartoon". Timmy gets through it safely thanks to Pappy and the fairies, but when Pappy describes it later, Mom and Dad decide he's senile and hallucinating.
- In Grandma Got Run Over by a Reindeer, Grandma is pretty savvy (at least until she gets Identity Amnesia), but Grandpa isn't quite all there.
Jake: (runs downstairs wearing a coat over his pajamas) Grandpa! I'm going to the North Pole to find Grandma!Grandpa: (calmly) All right; thanks for telling me.
- In The Powerpuff Girls, we have a classmate of the girls, Mitch Mitchelson and his grandmother, who is perpetually seen sitting in front of a TV set that plays nothing but static. Her grandson, meanwhile, is a juvenile delinquent in the making.
- Lou Pickles on Rugrats. Nine times out of ten, when put in charge of watching the titular babies, he'll end up falling asleep shortly after their parents leave. This was lampshaded in the movie after the babies got lost.
Didi: [angry] I can't believe you left them with your father! The man slept through Pearl Harbor, for heaven's sake!
Lou: I sounded the alarm as soon as I could.
- Any time Abe Simpson is left to babysit on The Simpsons, usually by falling asleep.
- He's not much better with the cat and dog either, asking them which one of them was the mailman.
- In one episode, Flanders adopts Bart, Lisa, and Maggie.
Homer: We leave you the kids for three hours and the government takes them away?
Grandpa: Oh, bitch, bitch, bitch.
- But he subverts it on one occasion when he uses subtle emotional blackmail to get Bart and Lisa to clear up all the mess they've made.
- A variation on this trope existed in the Spider-Man and His Amazing Friends cartoon, in which college-aged Peter Parker's dear, sweet, clueless Aunt May rented rooms to Firestar and Iceman (of the X-Men). Not only did she have no idea that her tenants and nephew all had supernatural powers, but she never noticed that they tricked out the house in such a way that would convert the living room into a sort of above-ground Batcave when they pulled on a wall sconce. Even more amazing, they did all these technological renovations while she was napping one afternoon.