On my most recent question a user in the comments has repeatedly been harassing and trolling me, and though I stopped replying, deleted my own comments back to him, and flagged the comments he posted as harassment and disrespect, only a few were removed. How can I ask a moderator to remove all of his comments?
Like F1Krazy said, posting on Meta is one way, though not necessarily the most expedient one, especially for things that actually require a diamond moderator.
Unless there's a need to discuss the issue, the best way is generally to raise flags either on the post the comments are attached to (a custom flag describing the issue in that case), or on the specific comments. If it's clear how the comments are in violation of the Code of Conduct, then a simple "harassment, bigotry or abuse" or "unfriendly or unkind" flag is the best, because those are treated specially by the system; but if it's not clear, or it's more of a pattern than any one specific comment, then a custom flag with a brief description is almost certainly better.
When reviewing comment flags, a moderator sees only the flagged comment(s), the beginning of the post the comment is attached to, and the flag type or (in case of a custom flag) description. If the same post or comment has received multiple flags, the number of flags raised per type is also shown.
To get the outcome you want in response to a flag, in general, you want to make the moderator's job as easy as possible. This means you can't rely on much surrounding context. If you flag just one comment as rude, when in reality it's a whole thread taken together that's rude, then the moderator handling that flag will look at the flagged comment, probably scratch their head for a moment, and likely dismiss the flag as not helpful because they aren't seeing the whole picture. Alternatively, the moderator might delete that one comment, but fail to realize there's a number of other comments which also need handling. Basically, if the whole picture really matters, then you need to say so, or the moderator won't know.
In this specific case, the community did a lot of the grunt work via flags that were handled automatically by the system, and I have done some cleaning up among the few comments that were left by the time I came along.
Technically, you're requesting that right now, but that's not what you meant.
If you want to clean up an entire comments section, the best thing to do is to flag one of the comments, select "Something else", and write a custom flag message explaining to the mods what you want done and why. In your case, something like:
Please remove all [user]'s comments on this question as they are harassing me with disrespectful remarks.
If you flag each comment individually, the mods have to handle each flag individually, and depending on the number of comments, you may end up drowning them in flags. I've seen moderators complain on other stacks that in these instances, they're unable to work as efficiently.