Blitz/MF bottom lane. I normally main either Wukong or Nocturne. So when people say "Hey, go Bot, and i see that the enemy team has a Blitz/MF combo, i'm fairly certain we've lost. Plus most times I play i get stuck with a ranged AD Carry like Draven. Who doesn't realize that Ever Blitz player camps the bush on bot. EVERY. SINGLE. BLITZ. So he face checks, gets grabbed and MF gets a free first blood. So now instead of going for assassin build, i have to Off tank, and build heavy Defense, which works into Wukong's move set and passive (gets Armor and MR for each enemy champion on him). HOWEVER. Once MF gets first blood, they almost always buy a BF Sword and start picking on Draven. I'll swoop in and ult to buy him time to leave and stop feeding, and god forbid i pick up a kill they spam my chat with "KSKSKSKSGO FK YRSelf Noobkong"
When i play Nocturne, if i can get some safe farm, i can usually shut down a blitzcrank with my ult/w/e combo. But most people Jungle with Nocturne, i use him in lane to bully. He's a good jungler, don't get me wrong, but his lane presence is so much more fun. A shield that disables ranged pokes? Check. A ranged DoT that turns into a stun if you stay in range? Check. A ranged harass that allows you to chase people down to use afforementioned DoT? Checkity Check. An ult that blinds enemy champions and allows you leap halfway across the map to slam into them for huge damage? Check. Let me get lifesteal and a frozen heart/Mallet and you aren't getting away anytime soon.
Other than that?
Scorpion spammers in MK9. Seriously, if you do that spear/teleport nonsense, and i block it and full combo punish you the first time, DO. NOT. KEEP. DOING. IT. It'll only get worse. Also stop bitching when i counter pick your fail ass with Baraka. Yeah, bring me in close. I LIKE IT THAT WAY!