Wild I'm usually with you, and I am on this one as well. We've seen too many situations develop into "self defense" scenarios when I would like to see what would have happened if the "victim" just called the police and kept watching TV. I would expect and respect him telling the guy to get lost the first time, but when its clear he isn't listening, why not call for help and finish your dinner?
Most harassment, repeated trespassing, and verbal threat related incidents stem from BOTH parties engaging in general obnoxiousness. If the guy had never gone outside, the kid never would have gotten killed. End of story.
If he still isn't charged by the end it would definitely go into the "moral vs. legal duty to retreat" bin. It becomes a classic case of a homeowner waiting for an opportunity to shoot someone.
I will throw one monkey-wrench into our viewpoint though (and BillCA did throw a few good ones as well). Police officers in many areas are trained to expect guns when they see drugs. This could extend to paraphernalia. Applying this logic could become part of defense to the actual shooting.