I don't think that rule sharking is a thing in competitive play

I think it's a thing, if we define rule sharking to be using the rules to influence the results of a game without adhering to the original intention of the rules. Or something along those lines.

For example: stackable sleeves. If you lose a round and then you call a judge over to say "hey my opponent has old sleeves which are stackable, please give him a game loss so we get a draw." That's rule sharking. Why? You are using that rule to influence the result as you have lost but now you want a draw. However, the intention of the rule was lost. The intention being that sleeves shouldn't be stackable, not that bad sleeves can give you a draw. You had clear view of his sleeves the whole time, yet you didn't say anything about it until you lost the game. This means that it was only relevant when you lost, not relevant the entire time of the game. If you had a problem with something, you should have mentioned it at the beginning. Then, the player can be forced to change sleeves if deemed appropriate by a judge before it can influence the game.

Another example: Moving cards after chains. Lots of players will play something like Kelidoscope and dump herald for unicore, and then search for herald. But wait! Kelidoscope is still in the s/t zone. JUDGE! Player did not complete the chain therefore he can't activate Herald (or some random bullshit like that that is completely irrelevant). I've actually seen someone rule shark like that and try to give his opponent a warning. The player is trying to give a warning and potentially a game loss by this rule. However, the rule's intention is lost (Chains must resolve before another card can be played). The player wasn't trying to break game mechanics, it was simply a pragmatic decision to leave Kelido on the board and search and then send all the cards to the grave. Very, VERY common in the yugioh community. It wasn't that he was trying to activate a card in between a chain because both players already know that Kelido has already activated.

That's what I would find to be rule sharking. Others may have a different opinion on that.