1000 things a dumb chess player would do

341. Hates chess.

342. Says every move is illegal

Is that possible?

343. Knock over their opponent's king when they win

344. Plays the Ruy Lopez... and yet they're below 500. 
But seriously. Ruy Lopez is super complicated. Against the Ruy Lopez, Black has over 10 moves that are all major lines.
345. Plays the Wayward Queen or Napoleon Attack
Again. People over-estimate this, and they lose tempo: your opponent can develop 2 knights, fianchetto the bishop, can fork you easily, and all you're doing is running the queen around. For opening traps, try the Legal or the Fried Liver. Worst if the French or Scandinavian is played after e4, as the checkmate doesn't even work.
346. Plays the Sicilian... and yet they're below 250
Sicilian is complicated. I don't play the Sicilian, but masters play the Sicilian more than the Open Game. 
347. Accepts the Queen's Gambit
Many think they get a free pawn, but White gets compensation: a full center, and wins the pawn back right away with the unpreventable discovered attack. Knights can't be developed to their normal square., If you see the Queen's Gambit as Black, play the Declined (e6), Slav (c6), Chigorin (Nc6), or something else.
348. Cannot win a 2 Queen vs 1 Pawn Endgame
If you have 2 queens and your opponent that has 1 pawn beats you or draws you, then you need to see a therapist.

For #343, that's very common, and not too dumb. Except on the computer, then yes, because you don't want to break a screen.

I didn't know it was so common :l I just thought it was rude to your opponent

No.

349. Thinks that they are a grandmaster after winning one single game.

351. Thinks his opponent is dead after he beats him.

352: you're me

353. Think that you're a baby.

354. Can find the only move he can make in check but refuses to make it because it takes their bishop

355 qqprupoiejfpwpejf

355. back rank checkmate because they were too focused on checkmating

356 wheqriuwepo

357 do stuff while playing a game while eating a computer while drinking water

358 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a.k.a saying pi (the whole thing up there) while playing chess