I think I have better advice for your specific request.
Lays down on the couch
I have social anxiety. As a result, I feel particularly stressed (read panic attack) in situations that most people would consider just a little embarassing, such as making a really dumb play or playing poorly in general.
Suddenly stands up, points at the ceiling and yells
I AM A POPSICLE!!!
coughs
I'm terribly sorry, this happens sometimes. So the solution I've devised over the years is to have humor prepared in advance for those specific moments. They are lines I can write in chat that will tend to defuse the situation or release tension. I have a mental folder full of them and I just pull one out as needed.
CATEGORY 1 : Blaming ridiculous things
"Damn communism"
"please report Teemo" (if there is a Teemo in the game, change the name to a champion who isn't in the game. Otherwise, always blame Teemo)
"If you had a cooler skin, this wouldn't have happened"
CATEGORY 2 : ridiculous excuses
"You only won that trade because a giant porpoise told me to let go. I thought she meant the keyboard, but it turns out it was just a pillow"
"Oh boy I made a mis.. no wait it was LAG!.. yep. that's what it was"
"It's really hard to play with these mittens"
CATEGORY 3 : Requests for abdication
"I surrender! Please just let me win"
"Can you please just let us win? Some of us have things to do you know?"
"Please just let us win, I once turned a man into a Newt!"
"Please let us win, my girlfriend said she would leave me if I lost"
"Please let us win, we really like winning"
As you can see, the dumber the better, but I guess that is a personal decision.