BIG Ben strikes 10 again!
I don't think there is much you can do other than abandoning your Guest Book or as you suggest edit out the comments.
This sounds like a wind up from someone who should know better and if he had a half a brain cell would be dangerous.
I might be wrong, but I don’t think this guy is all that young, the reason I am saying this, I will not see 60 again and we were taught to write a letter 'I' as a capital and if you have quoted correctly this chap has done the same.
Anyway don’t let idiots like this put you off, sorry I can’t help further.