Repost- add more reasons if you find them

- Never occurred to him that the Firebolt send to him anonymously could be sent by Sirius Black, who was, at the time still believed to be a murderer at large
- Tried the sectumsempra curse on Malfoy without knowing what it does, which is not very clever thing to do (and as he almost killed Malfoy, that showed)
- The fact that Snape wanted to see his Potions book after cursing Malfoy was a shot into an open goal that Snape had to be The Half Blood Prince. Potions books are not a very logical place to find curses in... unless Snape had written it into that book himself thus knowing the curse was in there.
- What was Harry thinking by writing in the blank diary of Tom Riddle? Of course Harry couldn't know Riddle was actually Voldemort, and that the diary was even a horcrux (since he never heard of that at the time) still it was kinda fishy to find a book that somebody tried to flush down the toilet with all pages blank.
- Pride prevented Harry from reporting the torturing that Dolores Umbridge used as "punishment". It was only obvious that what Umbridge did with that cursed quill had to be illegal.
- It didn't occur to Harry that the sole reason why his friends didn't write during summer was because their letters could be intercepted, since the ministry was clearly paranoid.
- Jump into an icy lake to get a sword. Even with "accio" not working there had to be a better way to retrieve the sword of Gryffindor.

Of course, Harry did not only do stupid things. He correctly deduced Malfoy was a Death Eater in book #6, and that he was responsible for nearly killing Kathy Bell and Ron Weasley, and that both had not been the intended targets, even when nobody wanted to hear it. (Of course, this time his intelligence came wrongly timed and it nearly messed up the planning Dumbledore had set up, but there was no way Harry could know what Dumbledore was planning and that he already knew that Malfoy was trying to kill him and that Dumbledore had already planned his own death. That would have been a miracle if Harry knew THAT at that point of the story).

Also, “my nickname is roonil wazlib” was not his best bet for success

That was indeed pretty stupid and very easy to see through. I do honestly think that the only reason that Potter wasn't expelled with that one, was because Snape knew how important Harry was in the entire setup against Voldemort. Had Snape not been secretly plotting with Dumbledore, I think things would have gone differently.

I didn’t know this was happening, thanks for telling me!

yeah.

tbh i think we can forgive harry for the half-blood prince's handwriting one, he lived with abusive guardians that only got him the bare minimum. if they could buy cheap glasses they definitely did.