Sonichu #1: Rosechu could have escaped on her own, considering she is just as powerful as the title character. But no, she willingly became the Distressed Damsel.
Sonichu #4: If Chris-Chan hadn't done... whatever it was... that got him suspect of solicitation, this issue wouldnt even have a premise, let alone a plot.
Sonichu #8: All of it. Whether its Sonichu confusing drawings with reality, Rosechu trying to counteract 4-cent garbages pornographic drawings with her own pornographic photographs, or Magi-chans inability to warn Blake ahead of time the danger he was in, everybody has dropped quite a few IQ points this issue and thats saying something.
Sonichu #9: Dating Education, starting from the fact that the title concept doesnt make any sense and only going worse from there.
Justified in the plot of Homestuck, as the main characters are kids and have to adhere to the laws of causality which make every single mistake they make required for paradoxes to not occur.
In Questionable Content, bad-tempered girl-with-issues Faye Whittaker takes the initiative and hooks up with her insecure boss Dora's popular brother Sven, who is famous among the entire cast as a playboy that engages in completely physical relationships with no monogamy involved. Throughout their somewhat antagonistic sexual relationship, Sven repeatedly tells Faye that it's just physical, and that he retains the right to have sex with other girls whenever he wants. Despite this, when he actually does exactly what he said he was going to do, Faye is crushed as if he had cheated on her, Dora is chomping at the bit to kick his ass, and the rest of the cast likewise treats Sven with disdain. The only character that didn't juggle the Idiot Ball in this instance was Penelope, who outright lampshades that nobody should have been surprised that Sven slept with another girl.
The entire plotline of 8-Bit Theater, so very much. Fortunately, it's played for laughs the whole way through and is an endless wellspring of humor.
Subverted by Achewood; Ray is incredibly foolish by any objective standard, but his impulsive and thoughtless (albeit confident) behavior is invariably rewarded by the rules of the world in which he lives. (He gains his initial riches by selling his soul, for crying out loud, which results in only a brief detour in Hell before allowing him to enjoy his riches for the entire run of the strip.)
The author of The Order of the Stick has commented that this is occasionally necessary for the sake of the story, usually in response to people arguing a more efficient way of doing things based on the D&D mechanics the strip universe runs on.
The strip is ABOUT the trouble these characters get in; if a tactic would result in an effortless solution to their latest problem, there would be little point in showing it, see? The characters are woefully inefficient as a result...
If the PC's stopped acting like... well, PC's for a few moments and just LISTEN to the NPC's, many of the series' problems could be avoided. Elan would never have been mistaken for his brother and arrested and Vampire!Durkon would have been exposed much sooner for instance.
It's also invoked to deal with Linear Warriors, Quadratic Wizards. The characters are high enough level that a well-built and played wizard and cleric would be so powerful as to render the rest of the team completely irrelevant. And so it is that Vaarsuvius has the worst possible school selection and tactics while Durkon insists on acting like a heals dispenser who sometimes remembers to use buffs.
There were... many, many problems with the now-defunct US Angel Corps. The least graphic of these were all the leaps of logic that comprised the premise: the US government reinstates a failed program from World War II, then addresses precisely none of the issues that doomed that program. They don't give their Spec Ops agents more than basic training (if even that), appropriate load-outs, any backup, or even armour. Then they act all surprised when things go south.
Narbonic: Played for Laughs. Since most members of the cast are Mad Scientists, the vast majority of the plots could be averted if they contemplated the consequences of their actions for half a second. It's to the point that Mell, a violent girl of average intelligence, consistently ends up on top simply because of her ability to think in a straight line.
Helen: It's at times like this that I question my policy of doing whatever dumb thing pops into my head.
Ménage à 3's plots are frequently driven by the fact that few of the characters are terribly smart, and even the fairly bright ones are prone to being driven by their hormones (this being very, very much a Sex Comedy). One notable repeated example is Gary's unwillingness to tell his colleague Tracy that he's not the sexual guru that she seems to think, and that he didn't intend to offer her boyfriend James oral sex, coupled with Tracy's muddle-headed attempts to manipulate the two men and James' willingness to believe whatever he's told (except that Tracy would actually like to give him oral sex herself). The stories involving the three of them are generally a mess of bad ideas and stupid misunderstandings.