you must not have even finished S1E1 yet.
My top 7 Stark screwups:
1) Leeana running off with Rhaegar and not telling anyone. This started the whole show. This is such a major plot point, that I will be a little pissed if the show never explains why they didn't tell anyone.
2) Kaitlyn kidnapping Tyrion with no plan of what to do with him was pretty stupid, and started the war between the Lannisters and Starks. The show points out how stupid this was repeatedly through the first season.
3) Robb Stark killing Karstark - this was a huge plot twist in season 3, and Kaitlyn, the Blackfish, and Robb's wife all tell him this is a bad idea before he does it.
4) Jon Snow charging Ramsay's army - Snow spends 5 seasons talking about discipline in battle, and then does something that stupid that almost gets his whole army killed.
5) Arya not ordering Jaqen Hagar to kill Tywin when they were at Harrenhal. This was a major screwup by Arya, and one that Gendry pointed out to Arya after she did it.
6) Ned Stark turning down Renly's offer for assistance while Robert was dying. Ned takes over if he accepts Renly's help. This screw up was brought up several times in season 2.
7) Kaitlyn and Robb walking their whole army into a trap at the Red Wedding. The show mentions how untrustworthy Walder Frey is every time it mentions him at all in the first 3 seasons. Watching the show the second time, the foreshadowing is so overwhelming that there might as well have been a ticker along the bottom of the screen the first 3 seasons telling us when and how the Starks were going to get slaughtered.
The show makes no secret that the Starks are a family of idiots, from the 3rd or 4th episode when Ned has Littlefinger pinned against the wall of his brothel, and after being released, Littlefinger says "the Starks, quick tempers...slow minds". In fact, the show tips hammers this fact home most episodes. Even in the Tywin/Arya and Hound/Arya arcs, the other characters continually point out to Arya that she is not nearly as smart as she thinks she is, and her and Bran are the smartest of the Starks.