There were even worse violations of logic and sense that season (::cough, Michael, ::cough::), but I know SGA is far from the only series of any genre which has given the characters collective brain damage when convenient. A more recent favorite of mine is another second season episode (and is there something about year two?) of Arrow, where despite constant and deadly hijackings, aid trucks continue to be sent into a destroyed and lawless part of the city with no protection and their logos clear on the vehicle sides.
But nowhere, nowhere, is this example of joint idiocy more prevalent than in any plot requiring a normally intelligent character to somehow not recognize another character in a flimsy disguise.
Arrow, of course, is a perfect example of this. And while I know that the whole show would collapse if Officer Quentin Lance ever noticed how very similar Arrow's height, breadth and the lower half of his face was to Oliver Queen, or if Laurel Lance ever recognized the enormous cleft in The Canary's chin as belonging to her sister, the absolute impossibility of this lack of recognition is both hilarious and irritating as hell.
I mean, we're not talking Batman-esque cowls here. We're talking teeny little eye masks with a wig and/or a hood. As an example, I made a hero of my own:
I know that none of you know him as well as I do, but seriously. How long would it take you to recognize him after speaking to him face-to-face day after day for several minutes at a time? And his nifty steampunk goggles actually make his eyes harder to see than the characters' eyes in the show. Quentin is a cop, for Pete's sake. His daughter Laurel is a hotshot lawyer. Presumably they'd be good at noticing stuff, like how similar those two vigilantes are to people they've known for decades.
Or if that's too much to ask, what about the fact that The Arrow and The Canary only appeared shortly after Oliver Queen and Sarah Lance returned from the dead?
And yet, the selective idiot ball keeps getting passed around. Maybe one day, Starling City's finest (former) Detective will actually detect that that Arrow guy is awfully familiar...