Ok Unticking all the boxes may cause a problem...
There are 9 boxes...
Tick NO.2 and 3 then all the boxes from No.5 onwards
What you'll have is NO buddy list but an IM alert activated when somebody tries to contact you. Can ignore them? answer them? or send their name to the block list? in 1 click ( Also see below)
There is also in the same area the "Privacy and Security" tab where you can block who is welcome or not? on a separate list if you are getting pestered?
You'll have to go into Parental Controls to make further adjustments ( Edit IM Control) only 2 tick boxes... Top box =stops chat .Bottom box=stops file transfers webcams ect. Your choice?

In case you are wondering? The AP in my name is Answerpool.com .(see profile)