Stupidity: Magnum and the policewoman do the stakeout and tailing for the drug deal using TC's chopper. A crooked cop that can't spot a helicopter on a nearby roof, a helicopter following his car, and most importantly, a helicopter landing right on the top of their apartment house building, should consider a career change or a hearing aid.
Forty Years from Sand Island - S3-E17
Stupidity: Magnum just assumes that the accident that happened to Higgins is an attempt to Higgins' life due to the earlier meeting, without even remotely considering the (he believes) drug dealers Magnum just messed with and that saw him drive away in that same car that gets sabotaged. Higgins never takes the Ferrari, so a sabotage aimed specifically at him is incredibly unlikely - as it's in fact the case. Just one of those things to keep the plot going.
Stupidity: After much buildup about the necessity to approach cautiously the KGB agent because she'd kill on sight, she does nothing of the sort; despite having intent to kill and putting her hand on the gun, she does not shoot Higgins or her assassination target, making the subplot about the infiltration pointless.
Stupidity: The whole episode has heavy farce tones and shouldn't be taken seriously, because the main plot point does not make sense; unless somehow he was able to produce remains of a body in the plane wreckage, Mr. MacLeish would have never been legally declared dead.
Foiled Again - S3-E7
Stupidity: Magnum hears from Carol that she's "sorry" and turning to the left he witnesses Higgins getting dragged in court. The two policemen who are escorting him stop at distance from the building, no obstacle or pressure, no reason other than providing a dramatic shot. (00:23:50)
Stupidity: Magnum saves Higgins from a scheme that was amazingly poorly planned to begin with; forgetting for a moment that as estate manager, Higgins should be very well aware of the closing time of 'the bank' (as if there were just one in Hawaii) even more than Magnum, Catherine could have not just relied on Higgins being this ignorant.
Stupidity: Earl Gianelli is a man on the run and can't ever show up as himself or the Mafia is gonna try and kill him, so he fights as a masked wrestler. However, for being a masked wrestler he removes his mask very casually backstage with no particular problem, unlike many masked wrestlers of his era who merely needed to keep their character and kayfabe, much less stringent reasons for them to do so than a permanent mafia death sentence pending upon them.
