First of all, this is NOT an official product by HLTV.org and there is absolutely no server side integration or any kind of special treatment.
so I made a extension to block annoying hltv users. To know how to download/install/use look at this page github.com/HRPsomenumbers/blockhltv
good things : you can block everyone (users, admins, mods, etc) and its for free
bad things : For now, you only can block one user and it does not works to match comments
and you still get replies notification and PMs from a blocked user.
Its for Google chrome.
if you find some error or any tip you can PM me.
You can change the code if you want but do it at your own risk.