The most negative you've gone.
I recently cleared a good chunk of a GUV using a GEE. I knew going into it I would probably kill myself with Mr. Grumbles as I always name them. Still I wanted to see how it would go. Pretty good unless he got fixated in trying to kill something he couldn't reach. I didn't have an way to reasonably deal with monsters except for the GEE and a wand of fireballs. Clearly this ends how you think it would.
He hit me with two criticals and ended up at -350 hp from about 250 hp to start with. I think I got -400 once from magic missiling myself against a wall with a post-game wizard from about 400 hp.
So how low have you gone?
Completed: All Races, All Classes. Twice.
Fastest Run: Dwarf Mindcrafter - 34803 turns. No wand of tele.
Challenge Games: C- CK (stupid ending), Platinum Girdle x10, Westside Story, Team Teleport - illiterate troll barb, Scroll of Omnipotence obtained
ULE - DE Archer