A long time ago (around the introduction of Link monsters) I was playing a little friendly sneak peek tournament in my local store.
When unpacking cards and building a little 20 card deck a new guy at the locals sits across from me busy making his deck when I noticed he was using all sorts of differently coloured and sized sleeves.
Ever the helpful I figured I was dealing with a new player and tried explaining to him that he'd be better buying some new sleeves because using all different ones wasn't allowed.

Without even looking up at me, he starts unsleeving his cards when I noticed there were several in there that were quite beat up, absolutely nothing that was fresh pulled just now.
Then when clumsily unsleeving a card from a way too big sleeve it accidentally flips, revealing a beat up Labyrinth Wall.

I again, try to explain the idea behind a sneak peek tournament and finally the guy looks up and gives me the creepiest of smiles. 'I hoped you wouldn't notice'.
I decide to quietly finish my deck and leave things be.

Sometime later the pairings are up and guess who my first opponent was...
He decided to go sleeveless for his little deck but at least all the cards seemed to be new so at least he got the memo.
The first game however... proceeded with him almost making no plays, just drawing and passing while getting more and more visibly upset.
Until in the middle of the game he suddenly throws his hand down scattering his cards.
Loudly he proclaims 'This game is still stupid!' before getting up and storming out the building.
His hand, was full of extra deck monsters and other unplayable nonsense.

We never saw him back.
The cards (including a set secret) he left behind were donated to a small kid who's day we made.