The episode begins with Patrick sandboarding, as he crashes into a hill, breaking into pieces. It turns out Patrick was playing a video game, but the same thing that happened to the character soon happens to him. Sandy warns SpongeBob not to play games and board, then SpongeBob begins to board. While sandboarding, SpongeBob does a stunt called "The Grouchy Squidward." While doing this stunt, he almost crashes into a tree. He then turns around to tell Sandy that everything is fine, but he then loses control of the board and is sent flying. He then begins to plummet to the ground, and Sandy tells him to land on his bottom. SpongeBob does so, but his bottom shatters into many pieces and he is rushed to the hospital.
Purple Doctorfish says that it took 20 hours to glue it back together and that if he has another similar injury, he may end up in the "iron butt" which is a huge machine on wheels connected to where the butt used to be. SpongeBob goes on "around-the-clock butt patrol," however it seems the entire outside world is out to break his butt, as he passes a football pitch where players are slapped on the butt, and a spanking machine. Eventually SpongeBob cannot take it anymore and decides to stay home forever with his "potato chip," the "penny" that has never been used, and a "tissue napkin" that has been truly used. Sandy and Patrick ask SpongeBob if he wants to go shuffleboarding again, but he tells them he will never go outside again. Sandy then says they will find an activity that is so fun, he will have to go outside. They try a cake that SpongeBob must leave the house to blow out the candles on, Jellyfishing, ice-creams, trampolines and even giving an old person a bath, but nothing works. SpongeBob then sings a song about the joys of staying indoors, which makes Sandy very frustrated.
Sandy comes up with a plan to have Patrick disguise as a gorilla, and pretend to attack Sandy, so that SpongeBob will have to come out and save her. SpongeBob is unconvinced by this until what appears to be another Patrick Star appears which transforms into an actual live-action gorilla. He then stuffs them into the bag, attacks them, and beats them up. SpongeBob initially does not want to risk going outside, but Chip 'reminds him' that if it was him being attacked by a gorilla, Sandy and Patrick would try to save him. Convinced by this, SpongeBob leaves the safety of his home to save his friends, but is easily defeated and is split in half by the gorilla. The episode ends with a massive non-sequitur: When SpongeBob asks how a gorilla can exist underwater, the gorilla says "George, they're on to us!" and runs away on his zebra as SpongeBob in halfs, Sandy and Patrick watch him and George ride away in the sunset. The characters watch them run off, and a family that watched it all in confusion turns off the TV.
SpongeBob's fear of danger outside his home is irrational enough to be considered agoraphobia.
SpongeBob's reclusive actions are similar to Howard Hughes. Although, Howard Hughes never left his house because he was afraid of outside germs, not injuries.
SpongeBob would not need to filter feed as he presumably has food in his house he could eat. However, it is possible that he is nearly out of food and will not go outside to get more food from the grocery store.
Before the "second Patrick" arrives, the real Patrick in a Gorilla Suit can be seen dancing similar to the Philippine novelty dance 'Otso-otso.'
"Yellow sand" is a reference to "yellow snow," since "Sand Mountain" is basically a Bikini Bottom version of a real-life snowy mountain.
When Patrick is about to hit the sand mountain, his sled disappears.
SpongeBob's butt should not have shattered upon impact as he is a sponge.
SpongeBob's X-ray shows he was taped up with a lot of tape, but the doctor said he put it together with glue.
When Patrick and Sandy enter SpongeBob's house, Patrick's right eyebrow flickers red for a fraction of a second.
When SpongeBob says "No problem," Penny, Used Napkin and Chip are missing.
When SpongeBob uses the really long spatula, the Krusty Krab clam sign is missing.
When Patrick closes SpongeBob's door, his arm goes right through it.
Near the middle of the episode, SpongeBob talks before his mouth moves.
Before the dust collecting scene his window is a circle, but after it is oval-shaped.
After SpongeBob sang "Indoors," Patrick can be seen crying. However, he disappears as Sandy points to SpongeBob.
Just before the old person says "I say we take a bath," SpongeBob's socks are missing.
When the old fish says, "I say we take a bath," the outside of SpongeBob's pineapple house is smooth instead of its normal texture.
Squidward is seen calmly watering his plants during the gorilla attack and SpongeBob freaking out with a piece of paper on his face. Squidward would have ran into his house as soon as he saw the gorilla, way before the viewers would even have a chance to see him. Or at least be watching in shock. The writers must have forgotten about the gorilla when thinking of the joke and decided it was so funny they had to put it in anyway.