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:
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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 ..."
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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.