In Code-E, Kannagi tells Chinami not to look at an ad with a couple kissing. Of course, she does, and due to her feelings for him and vice versa, her emotion-controlled electro-superpower gets out of hand and causes damage to the electric system of the bus.
In Rumiko Takahashi's Mermaid Saga, eating Mermaid flesh is said to give you immortality, and it can... but only about one in a thousand times. It almost always either kills you outright, or turns you into a gibbering homicidal monster.
She does it again in a Ranma ½ story, where Ranma (in girl-form) and Akane hit the tennis courts in relatively skimpy outfits (it's winter, so everyone else is bundled up) to lure out Happōsai. Akane mentions that the old man can't possibly be stupid enough to fall for such an obvious trap, but suddenly he appears, groping Ranma. As he's tied up, Happōsai complains that "Spotting a trap and staying out of it are two entirely different things!"
Happosai is notorious for responding like this every single time. It's when he doesn't that people realize something is wrong.
The Dirty Pair once had to deal with a trap that was triggered when one pulled on a little handle on the end of a rope suspended from the ceiling. The designer of the trap then proudly pointed out that it was a lot more effective than the "regular" stuff that burglars/spies/etc. promptly avoid.
"If I were to lose this key right now, we wouldn't be able to get inside the house!" Tomo snatches it and hurls it, later explaining that, "When you hear things like that, it just makes you wanna do it, y'know?" Once the key is found, Yomi has Sakaki physically restrain Tomo to keep it from happening again... especially as she thought doing so would be hilarious. Oh, Tomo...
She also does the old touch-wet-paint thing in an earlier comic.
Also playing with Mayaa, a wild Iriomote cat after being told not to. She gets severely scratched for it.
In the new years episode of Ninin Ga Shinobuden, Shinobu finds a button with warnings posted all around it, and doesn't even hesitate in pressing it.
In Dragon Ball, as the heroes find themselves in Pilaf's castle, they notice a series of lit up arrows on the ground. Their initial assessment of it being a trap is disregarded as being far too obvious a trap. It turns out to actually be a trap. Pilaf even lampshades this, "I never believed there were people THAT stupid."
In Slayers Next, Gourry pushes a button to disastrous effect. Later he finds another button which he doesn't push — when pushing the button would have deactivated the trap he then falls in.
Parodied some more in Slayers Revolution when Lina and Pokota cannot stop themselves from pushing buttons that say "do not push"; lampshaded by other annoyed members of the group.
Another Revolution example: Zelgadiss's trap for Pokota. It involves food, and an obvious cage on top of said food. Amelia is not amused and lampshades this trope. The trap works.
The "Lina Trap". The one with the unicorn horn, which is so ridiculously obvious that at a glance Lina muses that the trap must have been meant for Gourry (until Lina sees the unicorn horn inside the trap and promptly loses her brain). Although possibly Lina was the only one who would have fallen for that one. Even Gourry lampshades it.
Even Xelloss was not immune to Schmuck Bait. In an episode of NEXT, he comes across a shrine that says (paraphrasing) "Throw a coin into the fountain and ring the bell for good luck." Xelloss does so...only for the bell to fall on top of him in an especially ironic display of good luck (i.e. good luck is bad for Mazokus).
When the Straw Hat Pirates raided Sir Crocodile's casino in One Piece, they found a sign in the backroom corridors pointing off in one direction that said "Pirates". It led to a dead end containing a trap door which dropped them in a cage. Luffy considered it fiendishly clever.
Just a few minor examples from Hell Teacher Nube: Miki reads about astral projection... ends up turning herself into a Long-Necked Woman (permanently). She reads about "pulling" off your consciousness for an out-of-body experience... ends up trapped in the body of a female cat on the run from tomcats in heat. She hears a rumor about compelling other people to your will with their umbilical cords... Kyoko becomes her mindless slave and jumps off the school roof. She starts up a chain letter to con people into giving her money... she ends up bringing disasters upon the entire town and she's forced to experience the suffering of everyone she hurt as means of redemption. A few of her classmates also find playing with fire irresistible, but Miki is the worst one of them all.
In Mahoujin Guru Guru, Jaba kingdom has a rule that says that you must not stand in front of the guardian statue Pura Pura and tell it "Take care of your health" while boxing with your left hand, picking your nose with your right hand, and having a loaf of bread wedged up your rear. The prince Schmucked himself into getting turned into a pig as a result of violating this rule. Nike had to be restrained from doing so three times.
When you're a character like Eury Evans from Immortal Rain and you run into a door with "The Wages of Sin" and "Keep Out!" emblazoned across the front, are you going to keep on walking? No. Then there wouldn't be any explosions.
In the CLANNAD prequel episode, Okazaki and Sunohara make a party ball trap that drops a washtub on whoever opens it. The ball is opened by pulling on a tag that reads "someone please pull this, it will be interesting". Nagisa pulls the tag and gets knocked out by the washtub.
In Kaze no Stigma, a website temps browsers with the question "Do you want power? Yes/No". Answering "yes" will give you super-powers, but what isn't said is that this involves making a pact with a demon and all pact-makers will be used as sacrifices to summon a demon lord.
In Episode 8 of A Certain Magical Index, Touma asks Stiyl to stick out his tongue. When he complies, Touma uppercuts him.
Episode 7. Taro and several of the maids explore a mysterious underground corridor. They've already discovered that the place is filled with booby traps.
They encounter a rope suspended from the ceiling. Both Ryuuka and Ikuyo Suzuki thinks it's a pinata and want to pull it but Konoe orders them not to. Konoe accidentally trips and pulls it herself, then falls into an opening that appears in the floor.
In Hidamari Sketch, Yuno mentions having gotten the room formerly occupied by Misato, who had since graduated. Sae warns Yuno about a purple "snake". Back in her room, Yuno sees a purple rope, and decides to pull it. Misato had set it up so that when someone pulls it, a metal washbasin falls from a trap door, probably on the puller's head.
In Fate/kaleid liner PRISMA☆ILLYA, Rin gets a little too blinded by one position's absurd pay rate to notice that the job requirements are so specific that really only she could possibly fill them. Congratulations, Rin-san... you are now Luvia's personal maid.
Nichijou Yuuko convinces Mio to push the fire alarm button at school by telling her that she tried and nothing happened. The results are what you would expect.
In Infinite Stratos, Houki is looking at a pair of bunny ears is sticking out of the ground with a sign that says "Please pull me out". She doesn't do it, but Ichika does, and a giant carrot drops in front of him moments later. Inside said giant carrot is Houki's sister Tabane, who arrives in a less than dramatic fashion in order to give Houki her own IS suit.
One episode of The Melancholy of Haruhi Suzumiya-chan features Achakura wanting Nagato and Mr. Kimidori to stop being "carefree" and help her with the many chores. In one of the scenes, Nagato and Mr. Kimidori try to lure Achakura to a trap by setting up a piece of cake. However, it was a failure, because Achakura told Nagato to pick up her "things" and do some cleaning.
This happened to Mikuru in an earlier episode. At the beginning, Mikuru finds a remote, and what does she do? She turns on the TV using the remote, and the TV screen showed Haruhi up close and Haruhi says, "Mikuru, are you watching?" Mikuru then looks shocked. This became a meme, known as "No Mikuru! Don't turn on the TV!" In these memes, YouTube users who made the videos, in the title, warn Mikuru not to turn on the TV, but Mikuru does so anyways, and something appears on the TV screen.
Sword Art Online: Kirito's guild comes across a single chest in an empty room deep in a front-line dungeon. Played for Drama, since only Kirito and Sachi realize it's a trap before it's too late, and everyone save Kirito is killed in the ensuing fight.
Subverted in the Caliber side-story: The main characters encounter an NPC imprisoned in a high-level dungeon, who has her HP bar activated. Everyone assumes the NPC will attack them if she's freed, before Klein goes and frees the NPC anyway. Turns out freeing her is the only way to complete the quest.
During the "Terminator Maid" arc of Black Lagoon, Revy and Roberta prepare for a good old fashioned No-Holds-Barred Beatdown. Before so, Roberta points out that Revy's shoelaces are untied. Revy (whose shoelaces are always untied) thinks on it for a second... and looks anyway. At which point, Roberta promptly clocks her.