I know you mean well, but I have to disagree with your approach. Telling him to "stop" and "drop the attitude" is like telling an drug addict to "stop being such an addict".

It does not work.

It is a form of a "should statement" (a cognitive distortion) http://daphne.palomar.edu/jtagg/should.htm

In my comment above I listed a book to combat this.