What can I do about someone who first insults me via PM, and then spams every topic with insults and lies?

Your best bet is to block that person from pming you.
If the spam persists, gather the threads and pm them to the appropriate moderator of that section.

Block him and report the posts.

alrdy blocked after his second insult, but he spamming my topics with lies and others

Report the posts and ignore it - a moderator will be taking a look at their earliest convenience.
Don't respond to spam

In every thread, you have the option to report the post. Do that and don’t get into a discussion with him. The moderators will definitely take care of it.

well i did, so cant do more as it seems ty guys

I know it can be frustrating, but best course of action is to find a common ground and be cordial. If you just can't get along then go separate ways. If neither of those options work ignore it, report it and block them from pms.

I'd avoid spamming their topics as retaliation as that has a tendency to escalate things even further, it looks like you both are creating a lot of work for staff 'which I fear more'.

Who knows, maybe you two will be besties in the near future. I've seen it happen more times than you'd believe. Best to avoid being reactive in these types of situations.

Remember we all need each other to keep this site flourishing

just go sleep boy