You can only 'ignore' - go to their profile page and select the 'ignore' option in the top section. (Or do it on the pop-up when you hover/click on their name, in case you can't see their profile.)
Thanks. Not being able to see the comments helps but I'd really prefer if it blocked them from posting on my profile/auto deleted all their posts on my profile
If there's a legitimate case to be made for harassment, make a report. But I would be sure I'm confident that'll stand up to scrutiny before doing it.
If it's more a 'I don't like this person or their views/opinions/etc.', I don't know that there's much to do aside from steering clear (and asking them to stop if they chase you around the forums, which - if they don't - sets up a better case for the prior scenario).
Also, you'd have to ignore half the forum