Grace: Why not go through that gap between the buildings? Sarah: Hmmm, dark alley... night... two unarmed teenage girls... screams wouldn't be heard over nearby traffic... sounds good, let's go! Grace: Uhm, wait a second...
Subverted in Ursula Vernon's Digger by the eminently sensible and practical title character.
Traveling Merchant: Tell me, wombat — if I gave you a box and told you that it must not be opened, ever, under any circumstances, what would you do? Digger: Hmmm... Encase it in concrete, probably. Actually, I'd encase it in lead first, if the box materials could take the heat, then in concrete. Then I'd put it in the foundations of a useful public works project. Something they wouldn't be digging up again in a hurry. Grain storage, or mole dung composting... I'd have to check and see what was available... how big a box are we talking about, anyway?
The tantalizingly labelled buttons, "Yes" and "Hell Yes", in the last panel of this strip. Right under the sign "Do you need a laugh?" They're in one of Castle Heterodyne's pit traps.
Lucrezia's lab has a brightly colored gumball machine with a small sign above labeled "Poison! — brought to you by the Illiteracy Reduction Campaign."
A would-be conqueror by the name of X the Destroyer fell for an accidental bait when he assumed that the great big X in the fields outside Mechanicsburg was the place he was supposed to erect his pavilion while awaiting the city's surrender. Mechanicsburg's forces had mapped out every square inch of the plain in front of the gates centuries ago, and "X" marked the center of said plain.
More from Studio Foglio: The Winslow in Buck Godot: Zap Gun for Hire. A fuzzy, friendly lizard creature that happens to be the most desirable object in the universe, as almost every race craves to possess it for any number of reasons... and are willing to annihilate the current possessor, planet, race and all, to get it. Not dangerous in itself, but having it is bad for your long-term plans.
Cyanide and Happiness has a pretty good example in their animation "The Sign", where police beat anyone who reads a sign that says "Do Not Read".
Gadgeteer Genius Jyrras from Dan and Mab's Furry Adventures has a big red button on the control panel of his main computer, which, if pressed lock the whole system and displays the message: "Warning Idiot Detected By Keyboard"
In the "Forbidden Door" strips (this specific strip, and the next page, are clean); averted by the apprentice. "This is what, a moron trap? Fuck off." (Some other strips of that comics are Not Safe for Work.)
Also played with and lampshaded in "Tribute Day 2" (which is Not Safe for Work), where the Schmuck Bait is avoided due to the intended schmucks' heroic lack of curiosity — revealed after Mistress commented on such a trait being the only thing that would save them.
In Goblins, the treasure plant. The Treasure Plant is essentially a Man-Eating Plant mimic that uses jewels to attract victims. Only a danger to the stupidest of adventurers.
Dragon Mango: Free Meat! In the middle of a large red target. Next to a "Free Meat" sign. Directly under a sixteen-ton weight. And poisoned.
Claw: You let the princess eat raw meat off the floor?! Mango: Sorry! Sorry! It's just... well... Have you ever tried to get between that kid and a hunk of meat? Claw: Okay... I have to admit you have a good point there.
In thisThe Whiteboard strip, Roger is presented with a button with a warning sign reading "For the love of God do not push this button!", as a filler strip. Doc Nickel invited readers to suggest the results of pressing the button, and got several hundred replies (after expecting only a dozen or so). Strips illustrating the suggestions are usually posted on Tuesdays and Thursdays.
Dregs: The nudist falls for Mags's trap, which consisted of a jar of peanut butter sitting under an enormous, incredibly conspicuous cage.
The Hare's Bride: The hare's invitation. By all appearances he has in mind a life of domestic slavery and, if those teeth are any indication, possibly worse.
Discussed in Erfworld. An attack force approaches an enemy city that appears completely undefended. Two commanders of the force agree that their every tactical instinct screams that this is a trap but their only alternative is to turn around and flee because they weren't attacked. They press on, it is a trap, and they pay for it.
, El Goonish Shive does a Lampshade Hanging on the "dark alleyway" variation as an excuse for revealing Grace's secret:Grace: Why not go through that gap between the buildings?