Hearthpwn

conceeded on my 11th win in arena (when i had the game won already) when i wanted to go into options instead

Right there with you venom

My biggest recent blunder was having lethal on the board with Djinni and shieldbot.  Then casting Blessing of kings on the Djinni and coming up 2 short and losing the game.

Pressing the concede button instead of the end turn button when I had a fatigue lethal...

Pryoblasted my face in arena thinking on what card to play and was holding it on his face, hovered it over mine thinking it was back in my hand and clicked it on my face. :c was a longtime ago but still remember it today lol 

A while back I was playing against a Freeze Mage. I had lethal with Brawl provided that my boom bots didn't win or hit Archmage Antonidas. My opponent also had lethal next turn with the fireballs from Antonidas.

I played a bunch of minions to decrease the chances of the bad outcomes from brawl before realizing I didn't have enough mana to play brawl afterwards. 

I still haven't gotten over that mistake.

Got a wraithguard and a hellfire via thought steal op on 16 hp im on 30 i manage to play Played Malygos the turn before this turn i played a 6 mana velen due to emperor then proceeded to play hellfire at 3 Forgetting the effect of wraithguard i Ended up dealing 16 damage to my opp but then 16 then another 16 to me ... Rip took a little break from hs after that 

I'm not sure if it happened only me, but with combo druid, the savarge roar seems really similar to the shadow of naxxramas, I thought I have lethal few times :p

Also did with 9 mana grow of the wild 

And the best 1 which we all do when we ty to turn down/up the volume :)

Ohh , also we all counted our cards in hand  thought we have 9 and were tottaly shocked when a card was burned

Was playing as Rogue in the arena and had the exact damage to go through Belcher and win the game.

Turns out ordering matters, attacked with the weapon first, making it impossible for me to backstab it, lost the game after that :/

Ye olde Mistress of Pain + Auchenai Soulpriest. Good times.

Misclicked on my mobile once, and played lay on hands on a shredder instead my own face. Lost that game because of that.

Was going to play wrath on my opponents minion once. Played mark of the wild instead.

Playing Priest and used Holy Nova forgetting that Auchenai was still alive. Board wiped both sides.

Not so much an in match move, but spending thousands of dust to make an all gold Lock and Load deck, which I got bored of after about 30 games. It was pretty funny for a while though, Lock and Loading into Lock and Load and generating a bunch of random cards. Also a lot of the cards are Mechs which will be phased out, whoops!

I conceded by accident trying to lower my master volume. :(

I had 2 giants on the board and a BGH in hand, he plays dr boom and I grab my coffee, hit my table and target my own giant with the bgh.