I think the title and/or first part of this FAQ should be changed. Why? Because the answer to the actual FAQ title now ("Can I ban someone from reading my journal?") is a wholehearted *YES, my sistah*, you can ban someone from reading your journal. You use these handy things called security levels.
Granted, it's not a ban_set command or anything, but yes, you can prevent Timmy from seeing your stuff, which is in effect banning him. But the phrasing of the title/answer now is incorrect -- we're telling them they can't ban someone and then telling them how to do it.
So, I'd like to suggest the following:
1) I'd first suggest changing the title to "Can I ban someone from reading my public journal entries?"...
2) Then, I'd rework the beginning as follows:
"No. There is no way to ban a specific person from viewing your public journal entries. However, you do have options for achieving the same result through the use of security levels for your entries (http://www.livejournal.com/support/faqbrowse.bml?faqid=24). Friends Only entries, for example, effectively ban anyone who is not on your Friends list from seeing your entries.
If you make a public entry, it is visible to anyone. Banning someone from reading your journal ..."
Basically, reword the first paragraph to better state that they do have options, and draw the line between security levels and the 'banning' wording/concept. Then, move the 'public entry' sentence down as the beginning of the following "explanatory" section of the FAQ, as it fits a little better there.
Just a suggestion, of course. Others may have different/better wordings and so on, this is just a post to get the subject out there.
There would also be the possibility of reworking the FAQ to a 'How do I...' wording because of the "you CAN ban someone, here's how you do it" aspect of it. I didn't think about that one too much, but that would be an option as well.