ok, one more post and i'll attempt to shutup for a bit. ( note that i sad 'attempt!)
the talking about kicking another kid in the balls thing- either he was trying to impress you, or get a rise out of you. the best thing you can do, is not get into it, and not show any big response. the more power you give that kinda talk, the more he'll revisit it- to distract you from stuff he doesn't want to do, or just to wind you up.
i'd most likely respond to it by saying, quite clearly and in a pretty clear, but flat, distainful/disapointed voice 'thats not cool' or 'that doesn't impress me', while shaking my head a bit, then move right along- get straight into talking about something else- don't discuss it, don't be drawn in, don't get cross or fuss over it. just nip it in the bud and move on.
listening: don't expect the same level of attention span or conversation as you'd get out of one of your mates. little boys (and some grown-ups) tend to have a listening span similar to the memory of fish- about 3 seconds. most of us prefer talking than listening.
when you speak, try and be concise, clear, and relevant. know where you're going with what you say before you start, and get right to it. get his attention before you start speaking by making eye contact, and using his name right at the start of the sentance. make sure he's doing a good share (at least half) of the talking- he probably has to listen to his teacher all day already, and this time will feel like 'escape' time mentally from all that listening and paying attention- he'll wanna let off a little steam.