Kalista is the most anti-fun champion I have dealt with.
On EITHER team. Kalista's passive may as well read "auto-dodge skillshots" because that's basically what it is... and it's on a less than one second CD. Sure, a bunch of champions have a "get out of jail free" card, but at least a teammate can then follow up while that card's on cooldown.... but not against Kalista. She can just hop away again and laugh. Everything I know about skillshot flow is either champ walks out of the skillshot, tries to but fails, or burns a long cooldown to escape. Kalista's movements feel entirely alien to me.
This does not change when the Kalista is on my team. I had the absolute soul-rending terror of having to babysit one. The person behind the champion? Not a problem. This Oathsworn business is an unfair burden of knowledge on the wrong team. I watched the enemy ADC severely out-DPS my Kalista, then turned and ran - expecting Kalista to do the same thing as I've seen countless other ADCs do in the past when outmatched. NOPE! Turns out I was supposed to auto-attack Kalista's target for extra damage! And that would've given us a kill. How am I supposed to know that? It's not in any of my tooltips. Further, her ult demands that the support be (A) alive and (B) next to her. Therefore! Support just became 10000x less fun because now one champion is utterly forced to follow another for the entire game. Can't roam, can't anything. And, again with the ult, the Oathsworn has no say in when it fires - someone else presses a button and BOOM - you've gone from casting spells to using a Malphite ult...
I hate to say it, but Kalista is more hatable than Teemo.