One of Beavis and Butt-Head's primary sources of humor is the titular duo and other characters' failures at virtually everything, out of either stupidity, ignorance, or both.
- Oftentimes, adults won't notice a thing wrong about them (despite having "stupid" written all over them) and give them jobs, such as Tom Anderson, learning their true nature the hard way. In Anderson's case, the boys manage to take advantage of his senility and get jobs from him repeatedly.
- In "No Laughing", the Spanish teacher asks the duo what several words are in Spanish. All Butt-Head could come up with are the words "burritos" and "guacamole", while Beavis comes up with "spaghetti" (an Italian word). The exasperated teacher states to Beavis and Butt-Head that the only Spanish they know after almost an entire school year is what they learned at Taco Bell, adding that Beavis can't even get that right. He orders them to come up with Spanish sentences, but Butt-Head spouts some vaguely Spanish-sounding gibberish ending with "Rico Suave", and Beavis says "Taco supreme", sending them both to McVicker's office.
- At the end of "Woodshop", Beavis gets his sawn-off finger reattached. He attempts to pick his nose with it, only for it to snap back off.
- In "Green Thumbs", the pair try to make their own Counterfeit Cash at a copy store via photocopying. Said cash is one-sided, printed on ordinary paper in black-and-white, and cut extremely poorly. Beavis even tries to counterfeit nickels. When they try to spend their fake cash at a store, the clerk is not fooled at the slightest and angrily tosses them out, leaving them to go back to the copy store and try spending their remaining fake cash to make more fake cash.
- "Sprout" sees the boys try and grow a plant as part of a class assignment, hoping to grow their own nachos. The two wait impatiently for their plant to grow, and Daria has to tell them how to grow it properly. Even when they try to follow her advice, they refuse to water it, claiming that "water sucks". Even after the duo stomps the seed packets into the ground, feeds in junk food, and yells at it to grow quickly, the seeds only grow into a single sprout.
- In "Special Delivery", Beavis and Butt-Head are in charge of Burger World's first delivery service. Of course, it ends up in complete failure — the duo not only gives food to the wrong house, but they don't even get paid because the guy had no money. Burger World is also overcrowded with angry customers due to the duo's absence. The manager had to discontinue the delivery service immediately, with the duo themselves being none the wiser.
- In "School Test", Beavis and Butt-Head spend three hours writing their names.Beavis: Yeah, I wrote my name too. See? Beafis. Now, wait a minute. That's not right.
- Their stupidity reaches a new level in "Trouble Urinating" in which they forget how to pee.
- Beavis and Butt-Head don't even know their own address, as shown in "Prank Call".
- In "Ding-Dong-Ditch", the duo tries to pull off the Ding-Dong-Ditch Distraction. However, all their attempts fall flat:
- In their first attempt, they don't run until after the homeowner opens the door and sees them.
- In their second attempt, they forget to ring the doorbell.
- Their third attempt sees Butt-Head run this time, but Beavis still forgets.
- When they do perform the prank correctly, the family at the house has just left.
- In "Pranks", they try to egg a house. They completely miss every time, and when they get more from the owners of said house, they simply throw the eggs on the ground. Then, they attempt TP'ing, and throw a roll at a tree... but it lands down a sewer. After they're given more and do it successfully, they find out about the supply chain issue that caused a toilet paper shortage. They try selling the toilet paper they get off the house, only for the owners to assume they're doing something nice and throw it all away.
- In "Stolen Valor", the old Beavis and Butt-Head (posing as veterans) are asked to hang an American flag on a flagpole. They instead take an old Viet Cong flag and fly it over the American Legion hall, thinking it's an American flag. The real veterans (Anderson among them) realize that the two aren't veterans at all, promptly beating them up.
