Jungling as it stands.
Currently jungling is one of the most unbalanced things in game, it's on par with the tower dilemma. It also doesn't help that the leveling system is bullshit.
There is no reason that: A Lee Sin, should be able to gank at level 3 with only a hunters machete. A Rengar should be able to 1v2 or 1v1 virtually anyone, at level 3 to 10. Any jungler should be able to camp lane and give the excuse that they were just helping their teammate. That's harassment and unsportsmanlike.
I get that Riot like to balance their game around LCS, but they need to look at what's happening to the 99% of players, since that's where all this takes place.
Small PSA: If you are a jungler, please, don't be a prick.