How do I stop nasty comments about my posts?or
How do I block a person who posts nasty comments?
My answers always start with
You can identify your commentors, using a properly chosen visitor counter / log utility.
When you have identified the IP address in question, use IP Address Blocker (free) to prevent access, from that IP address, to your blog.
Simple enough? No. There are definite limitations to the effectiveness of this process. And, Blogger can provide limited assistance, only. But, you are allowed to try.