For me it was when I first started playing the game, I was a warrior and I was putting on cloth, leather, and mail gear because it had a higher ilvl. Yet I didn’t know yet that stats were different for the armor types, along with using the incorrect weapon types because I thought they were cool.
What’s your noob story that you have?
Open the vault in the wrong spec
OOF that one had to hurt bad!
I was once tanking Skyreach on my monk and used Zen Pilgrimage instead of Zen Mediation during the third boss.
Edit: Third boss, not second
I was mad until i got a vault with appropriate gear.
Played ret pally in Wrath. Still embarrassed
i thought sitting down in classic regen mp faster for a long time lol
Back in WoTLK my first char was a hunter. I played with a polearm all the way up to ToC. No one, not even my guild members, told me that I needed to use a bow. I pretty much leveled and geared using traps and my pets, while I just whacked away with my polearm.
Trying to run from Theramore to Darkshore back in Vanilla. Not a great idea.
Reading and posting on the forum.
LOL, so you NOW play a class countered by both.
I started a night elf warrior during wrath and followed a general guide on how to level. I used Shadowmeld to avoid dying and had no idea what the stats meant in the game. Even dungeons sounded like some deep dark chamber deep in the earth some alien dragged me into that I had to fight my way out of.
At the low of Season 1 - I was going back and getting mounts I missed while away during BfA and SL.
I saw the slime serpent and was like, “sounds easy enough”. I set the difficulty to mythic and went to solo the dungeon.
Went back up - and no serpent 
I did it several times. On several toons. I swam in the green pool to get that moving serpent to see if it was clickable.
For the life of me - there was no slime serpent!
I went to the secret finding discord, Explained what was going on. They thought it was weird. They gave me very verbose instructions. I followed them.
No slime noodle >.<
I then submitted a ticket and got the most unhelpful automated response and pointing me to WoW Head and the Secret Finding Discord.
This mount was NOT DROPPING on mythic and I swore it was bugging out.
Then - one of my friends had me double check, “the Dungeon difficulty is on mythic, right?”
…Turns out, I had set “Raid difficulty” to mythic…and dungeon was still set to normal…
And uh, slime noodle of course doesn’t drop on normal mode. So, uh, yeah.
LOL well at least you got it!
On a side note I remember doing that back in BFA, it was a pain too but it was fun.
I came from Runescape right before this game in 2005. My first character in Teldrassil i was running around trying to figure out the game and some other person kept trying to duel me so I kept running away because I thought if you lost or died you dropped all your lootz/gear and they took it lol.
My husband and I were trying to do the Love holiday quests back during WotLK and were horribly under leveled. After being attacked by spiders thirty times we decided to call it quits.
When I very first started playing back in Warlords, I queued up for Everbloom as a tank. This had to be my first dungeon and I left after the 1st boss was killed because I thought killing one boss meant you won or something. I’m sure that group wanted to kill me afterwards.
Feign Death on Fangkriss(name?) in AQ40 on a wipe, while everyone was zoning in I accidentally moved triggering boss aggro. Everyone who was inside the instance got teleported in front of the boss and insta-gibbed.
This was not WoW Classic, this was real Vanilla WoW.
This had me laughing, I’m so sorry! The re-running and going through that process must’ve been sooo frustrating. Glad you got it sorted.
Played Death Knight in pvp since Legion instead of maining ret paladin