Fabricator-general shows something

The feedback button is one way, in comments you can flag them, also you may block them. Blocking obviously does not report them but it will spare you the agony of their existence.

I actually had a conversation with OlympianProduct about this back when I was new, currently there is no way to flag a user.

The community and global mods see all flags, so flagging any content that violates the TOS will make the mods aware of this person. If they are consistently harrassing you, flag the harrasment, block them and be on your way.

No, but you can block them