It looks like this profile is the current winner for most negative:

https://news.ycombinator.com/user?id=Proven

The TempleOS guy was probably one of the more memorable ones though you'd need showdead on to see a lot of the comments from his accounts:

https://news.ycombinator.com/threads?id=templeos https://news.ycombinator.com/threads?id=TerryADavis https://news.ycombinator.com/threads?id=losethos

Posted a lot but had fairly meagre karma.

Some background about him: https://news.ycombinator.com/item?id=23112887

This prompted me to look. Could not find too much though I found this post suggesting that it can go negative. I would assume at a certain point your account would be banned so maybe there is a cap. Personally I would be surprised if these folks had websites. https://news.ycombinator.com/item?id=9179609

Yes, it does, although karma on any individual comment is capped at -4 and if you keep posting them you may have moderation action taken against you.

as mentioned, tdavis certainly deserves recognition on that front

reddit used to have a 'sort by most controversial' (iirc just downs plus ups) that bubbled the most interesting comments to the top, apparently they were going for types of users who weren't into that though