For me, it changes from time to time, but I find the target of my hatred eventually circles back to one in particular over the years.

And it really isn't so much his kit.
The fact of the matter is, I usually only ever face him when someone who actually mains him is playing the champion. And they play him extremely well whenever he's my opponent. And it makes it extraordinarily annoying and frustrating for me.
It's not like a Yasuo or a Zed or a Yi or a Vayne. Sure, those guys can get fed and then carry a team to victory, but I still have a 50% or greater chance of any one of those champions being piloted by someone who can't actually play the champion well on a consistent basis.
But not Shaco. It's almost always a seasoned Shaco main, possibly a smurf, behind the wheel of that particular champion.