I think chucK's got a point. Save your energy for the serious stuff...you might think sloth and apathy is pretty bad (and I'm sure it is hard for a parent to deal with, especially since you & your wife are so active yourselves), but it could be worse, like he could be getting arrested, hurting others, whatever.
On another point, I think a trekking vacation in Tibet sounds awesome, but it's probably the last thing that your son would be into right now, judging from what you've said about him. And it wouldn't be much fun for you if he wasn't into it. Save it for 5-10 years down the line when he realizes that you're an OK guy after all.