What was your worst misplay?

[Aetherium Slinky]

Two cases of really, really bad blunders.

We had a pod of: Ertai, Wizard Adept (me), The Council of Four, Rona, Sheoldred's Faithful and house ruled Tamanoa. Tamanoa goes for a massive Earthquake and for some reason I totally forgot Tamanoa gains life and that my game plan is mostly untappers on the ground. I had Ertai, Wizard Adept untapped and ready to counter a spell...

A pod of: Kami of the Crescent Moon (me), Lazav, Dimir Mastermind, Oriss, Samite Guardian and Subira, Tulzidi Caravanner. I decide to play Ancient Silver Dragon without any protection. Guess if a certain Lazav, Dimir Mastermind smacked me to death with commander damage with their new shiny dragon and if they also drew their entire deck and won the game?

I don't know what's been up lately but I've been making absolutely horrendous decisions.

[Morganator 2.0]

I never make misplays

[Aetherium Slinky]

I never make misplays

What started as an obvious joke has now become a burden I must carry. Gee, thanks.

[WWolfe]

Playing my Skullbriar deck, down to me and a Prossh deck. He sacs enough creatures that he is able to make Prossh a 23/23 and swings in for the win with commander damage. I have no flyers and thought no tricks up my sleeve so I concede. When I'm picking my cards up, I realize I could have used Retribution of the Ancients to remove enough counters from my creatures to kill Prossh and survive. 

[Landale]

I was playing my Delina, Wild Mage deck against Willowdusk, Essence Seer Aminatou, the Fateshifter and Raggadragga, Goreguts Boss.
I already took out Aminatou and Ragadraga, but by then I was down to 9 life after Willowdusk boardwiped with Deadly Tempest and they still have their Sapling of Colfenor at 9/12, they then drop in a Bloodthirsty Aerialist as well.
My turn comes around and I draw into Barbarian Class and have enough mana from treasures and lands to play it, max it out, get Delina out, give her unblockable with Access Tunnel and swing in. At this time I also had a Glittering Stockpile with 5 counters on it and Spinerock Knoll with a Sarkhan's Triumph in it. I planned out perfectly that I'd swing and if I managed to do enough I'd crack the Stockpile after searching out Wrathful Red Dragon and it all goes off perfectly, they're even down to 8 life at this point... Except I tapped the Stockpile to pay into Access Tunnel instead of using a Mountain. So no blocker that would kill them for me and I lost.