While Rickon did have a bit rougher of a go than Joffery, he wasn't some seasoned vet.. he was still only 6 when he left Winterfell.. how much could he know? He wouldn't have had much, if any combat training.. the only thing I remember him doing in the show is running away from things. Even with time in the show being skewed, he'd be what? 12 at the oldest? He wouldn't be applying any adult thinking, let alone having any idea what to do when people are trying to kill you. Another thing, it's been well documented that people in panic's vision can go into tunnel vision mode, so again, it's very possible that he didn't even see anything other than Jon on his horse trying to save him. Out of all the odd things, the dogs waiting to eat, the fact Sansa knew what Ramsey said even though she had left before he said them, the fact that Sansa was in the tent while they talked about their plans yet said nothing, only to turn around and give a speech about how no one was listening to her.. the fact that Jon charged the army on his own, the fact the giant was able to tear down the gates of Winterfell even though it had been said it was the strongest fortress in the north.. out of all these things, the only thing that could be possible is the one that people glob onto thinking it's totally bullshit.. Read blink by malcolm gladwell.. he talks about how some people react in fear.
Edit: Also the arrows were coming from behind him.. he hadn't a clue where they were going to land.. unlike Bush who was looking right at the shoe coming at him..
We saw Bran scaling towers in the very first episode. And in the flashbacks, we see the young Starks training young. I always got the impression the Starks were tough SOBs, and they started young. Even Arya. The only exception seemed to be Sansa. Also, Rickon was on the run for at least a couple of seasons, so you would think he would be in survival mode.
I also thought we saw Rickon see either the first or second arrow, so he knew what the deal was. We all know he was going to die no matter what, but that was maybe the dumbest way to do it.
Whats funny about the Sansa thing is that Jon asked her point blank about her thoughts on the plan and she was super vague. I wonder if that was on Little Fingers instructions. I have a feeling the Knights of the Vale would have always shown up at the last second when both armies were decimated. And when they said the gates were strong, I dont know that they were thinking giant proof. Especially a pissed off giant. Jon rushing by himself was dumb, but one could chalk that up to rage. I could understand the rage more than being so afraid that you forget to avoid the thing you fear. And in general it seemed like Jon was resigned to dying. Out of all the dumb things you listed, running in straight line to avoid arrows is the dumbest! Its similar, although ultimately not as significant, as Arya taking a stroll down town while being hunted by The Waif. Its just dumb, and it could have been handle much better. In fact, sometimes they do things so dumb the internet goes crazy trying to make sense of it, and in the end, it was just dumb. lol
Its the failures of common sense things that break the suspension of disbelief and stand out more. I mean, who really knows how strong a giant is, and people can understand being so enraged you go in a straight line after someone. But avoiding something being hurled at you...most people can relate to that. Maybe if I've known fear to the point of literally shitting my pants I'd think differently about it, but I dont.