World of Warcraft! Jk
I'd say Diablo3 Inferno right after release - Everything is going to oneshot you? Ya, I liked that.
Oh yeah, I forgot about that too. I gave up on D3 Inferno after Act 1. Was fine all the way through Act 1, but then when I got to that desert area, I just gave up on it after like my 5th death in a row. That shit required far more patience than I had.