I forgot to screen shot this when it happened. But in the loading screen after we got a full team in TB I was just thinking "oh-no, this sucks" I was the nami.
Our team vs Enemy team
top: Garen vs Renekton
Jungle: Evelyn vs Lee Sin
Mid: Lux vs Fizz
Adc: Vayne vs Cait
Support: Nami vs Taric
When you decide to dive top lane and 3 enemies pop out from nowhere. "Maybe this was a bad decision"
When I play against a hit-and-run sort of champion, or an all in that dodges a ton(cough cough 
cough), or 
AP. I played against on yesterday; it drove me insane. I was diana, she spammed e and basic attacked, then ran when i engaged. And If I ulted, here lemme jump and YOU WILL EAT MY ULT AND DIE.
I just lose it sometimes instead of focusing on catching up.
When they counterpick teemo to your nasus.
When they pick 
to counter your 
my most recent "oh no" moment happened just yesterday. I was playing Leona Supp and had seen the enemy Skarner, Ahri, and Lucian heading past their (purple's) blue buff to purple's tribush just past the first bot lane turret. My Cait was pushing lane while farming, and we quickly we reached the place I had seen them disappear (the first turret was down). I went to ward the tribush like normal, but in the time between pressing the trinket button and the actual ward coming down, I realized that they still must be in that very bush. I had just enough time to think "oh, sh--" before the ward revealed them and they came flying out, killing us both.
Using an execution ultimate (looking at you Darius and Garen) on a clone. Really grinds my gears.
When season 3 started with more server problems than usual.
biggest oh-no moment was last week. Team was making a solid defense, then we all died.
oh no. another game lost to b5.
enemy team rushes our nexus, and we all respawn just in time to save nexus and kill them all.(i was ziggs, mega-inferno'd the crap out of them), and then we came back after a solid defense, and won the game.
biggest YESSSSS moment of my life.
