Exclude a "user"

Last night a friend of mine came over. Over a nice cup of coffea we started an academic discussion of the Internet. Then he asked:

"I have a (theoritical) website , www.zzzz.yy and somewhere in the cyberspace is a "user" called "annoying_user", who fills the tables with spam. Excluding the fact, that the web-site code is badly coded, is it possible in some way to track his/her IP-number, his server-address, record this (file , database) and next time he/she (the annoying user) addresses my page (www.zzzz.yy), he/she (and only he/she ) will be met by an excluding page (eg. HTTP 404), so I don't have to "clean" the tables each day, and how do I do that - if possible ? "

I could not give him a good answer - can anybody here ? (REMEMBER ACADEMICAL QUESTION !)