My mother always says that she heard a speech about raising children by the Torah Umesorah Convention a handful of years ago that was a tremendous eye opener for her. I wish I knew the name of the speaker who said, “We don’t raise children for our own gayva. Raising children is not about what they can do for our self-image.” About myself, I remember the arguments before then when I would yell at my parents telling them that I felt that they only cared about me if I was able to show the world what good mechanchim they were, and I remember feeling the difference when I felt my parents were no longer ashamed of me but were willing to accept me even though they might have felt judged by their friends.
Although I am no longer a teenager, I was one recently enough to understand the mindset. The more you view him as a major disappointment instead of a nisayon from Hashem, the more there will be fighting and the less he will care about your cause (i.e.-playing it smart in front of the neighbors). The more you yell at him, the more he feels he has to be rebellious; it’s possible he even feels hated. If he wouldn’t feel the tension coming from his parents, he wouldn’t feel the need to fight against it.
It is a primal instinct to want to feel pride from one’s parents but all he feels is rejection. Even buying him cigarettes won’t do anything if he feels that you hate who he is as a person. He is going through way too much pain right now to care about religion, and he for sure has negative interest in having the neighbors admire his level of observance. The longer he feels like you view him as an embarrassment, the longer he will reject anything you represent. Furthermore, the more he feels like you view him as a failure and are embarrassed of him, the more he will feel that he has to do actions that justify your feelings toward him. To explain, he knows that your feelings won’t change as long as he doesn’t xyz (things that are way beyond him right now), and he knows that even if he made limited strides in that direction you would still feel embarrassed. Therefore, it would be too painful for him to do that effort (which you would view as a little and for him would be mountains) and still be rejected, so it’s much easier for him to do things that will make him deserve your feelings rather than attempt the impossible.
Btw this is a really good video if the mods will allow it. http://www.youtube.com/watch?v=tx-XpZDdyjw