My worst group consisted of the same person over and over in all of my groups. This is the legend of Sasha Gray (yes, named after her).

This was back when the game was fresh and Titan EX just came out. Garuda EX I cleared after some troubles, but at least it was doable.

Now I'm super pumped to try Titan EX because it's normally such a fun fight. I queue up and see Sasha Gray in my party, and I chuckle a bit. We get through some of the fight and I see her fly off the screen into the abyss. No big deal, there's a lot of stuff to dodge and the servers are spotty. We try again. And again.

We eventually decide to abandon the duty because a few people kept falling off.

So I queue up again and lo and behold, Sasha Gray is in my party again. As expected, this dude just can't dodge landslide to save his life. We disband again. I rejoin queue 2 more times and each time there she was: Sasha Gray. My own personal cockblock.

I eventually got fed up and quit, leading to my 3 year break. I still never beat Titan EX.

TL;DR Sasha Gray rammed me in the ass and made me quit the game