Have you ever done something great in a multiplayer game and then ruined it doing something stupid?

I got a pentakill in League of Legends and then dived under the enemy tower cause I knew that at that point in the game I could take it down on my own-- except I didn't notice I was pretty much about to die (one hit from the tower was all it took) ^_^

I'm bad at multiplayer games in general.

I've done something stupid, then something awesome to redeem it?

One time I was playing CS:GO, which I really suck at. I died most of the time, but during one match, after planting the bomb, everyone on the team died, leaving me to defend the bomb against one other player. We were both circling around a container thing, and for some reason, I managed to kill the last player of the enemy team with my pistol without dying.

Felt nice to be congratulated by my team for my skills, although really, it was just crazy luck. First and last time I was ever decent at a multiplayer game.

no, it's usually the opposite, then i get insulted and leave.

I once saw the exact opposite:

View attached image.

I've done something stupid, followed by something even worse, does that count? I have absolutely no game sense sometimes.

Sure.
Been playing Counter-Strike since forever, I've had countless games where I could kill the rest of the opposing team in great fashion, only to whiff every shot on the last guy and fail miserably.
Or have games where I suck most of the game and then have a round or two where I "pwn" the other team.
The latter happens more often these days, since I'm often sucking with my old-man reflexes :D

Way way way back in the day, I was playing cs1.6 at the WCG 2002 in Seoul Korea. The previous player had changed all of the key binds on the stage computer and when I went through to check settings I skipped over the use key. First round as CT on D2, the T's rushed A, I did a quick rotate from B through tunnels and up on catwalk, got 4 pistol kills and went to defuse.... nope - E was no longer +use. I would have won the round easily, but fumbled with the console pull down and typing the bind so ended up losing the round. We did ultimately win the match but it was a pretty rough start!

Black Ops 2 Zombies.

I turned the power energy on tranzit mode and everyone died because i didnt know what would happen if i pressed it again. We where +30 levels on it.
Everyone raged at me :(

Fucked up multiple times at Rust too... a lot. Oh, and minecraft too, and CS:GO too, and and...

GTA 5 too, i fucked up the last heist and we all lost because I died, so we didnt get the 1Million $.

I have some stories to tell: Once I was playing CS GO, so I bought a nice AWP and went to my spot. I killed 2 terrorists before they threw a smoke grenade. Then I shot twice at the smoke and killed a 3rd terrorist. I was so excited that I started to type a chat message... and got shot in the head.

And this one happened today: Someone invaded me in Dark Souls, and after saying hello to each other, the duel started. Both of us received a lot of damage, we only needed to land 1 more hit to kill the other. So I switched to a talisman to use a spell, only to realize that I ran out of charges... The other guy took the chance and killed me with a simple R1 slash. I felt like an idiot after that.

Edit: Awch, that play of the game :p It was pretty good until the part when you fall of the cliff :/

Likely had lots of these in Dota 2. It's not at all uncommon there for little mistakes or bad luck to turn an amazing plan you had into a disaster. You can be sure my teams nearly always remember the mistakes and never the good bits. :|

Since you used Overwatch as an example, I've jumped off a cliff by accident at least a few times in Team Fortress 2. Whether it was after something awesome or not is up to your imagination. XD

Pretty sure we all have our moments, nobody is perfect, and there are countless minor variables that can tip the scales immensely.