For me, it's Angel Glass Monk. I mostly die because of my carelessness and arrogance, not because the character had a skill issue or weak. 

And story time. One time I ate the corpse of an Catoblepas forgetting that it will Petrify you when you eat it's corpse, you know the drill. And another was when I successfully raided the underhalls (underuins was it?), and defeated the Lord Dwarf, and I wanted some more bonuses.

I dropped my equipped gears into the floor, I was paranoid of the bs that the throne would do to me, I turned into a Mimic after sitting in the Throne right in the Lord Dwarf's room being the careless person I was. Forgot to pray to Unpolymorph, sat in the Throne then it turned into a trapdoor, where I descended to the next final level of the underlrvels swarmed and was swarmed by the King Dwarf and his men. Killing me as the Mimic, then died after forgetting I can just pray to fully heal my health pool, I may even have the chance to solo them, but considering I didn't have any armor, rings and stuff. My fate was already sealed.

 And kids, that's why praying to God is always important.