I use uBlock Origin for this, something like:

  news.ycombinator.com##:matches-path(/^/item\?id=/) tr a.hnuser:has-text(/^dpifke$/):upward(tr)

This mostly works, but only kills the user's comments and not replies, so it sometimes can be confusing.

  news.ycombinator.com##.default:has(a[href="user?id=dpifke"]) .comment