The woman's comment just means that she is impressed by the French horn. A 'bad-ass' is person who is cool, confident and stylish. An object which is 'bad-ass' is something that embodies those qualities.

Rei, why are you watching such rubbish? It ruins your English and your manners (I saw your "What the hell" bar pick-up question too).

Here is how you should respond if you find yourself in a similar situation: "Poor horn! It would have hated being bad-ass!" If she retorted, "What's wrong with that?" Then you should respond, "Do you remember what the Queen Mother said about Cool Britannia?"

If you believe in Freud, or D.H.Lawrence, then it is a sexual reference. She needs sex and she is trying to arouse her date by drawing his attention to a phallic symbol, the horn, using the slightly vulgar and suggestive "bad ass" to highlight her admiration and desire. The colour "blue" is deliberate to remind you that you are watching a scene from a blue movie. The reference to "ass" draws his attention to her buttocks. It is the American way of doing a family-hour Japanese sex video in words on television, except that everything is coarser than in Japan.

I agree. 'Bad-ass' is informal AmE, but it is not a 'profanity' and it isn't even rude. It's a recommendation.