Season 19, Episode 15
Lisa takes up ballet lessons after Marge fails, but her skills are weak. Encouraged by the other girls in the class that the secret to a good performance is smoking/breathing in second hand smoke, Lisa finds she has no choice but to engage in the habit - much to the disgust of Homer when he finds out.
There is a scene where Bart emerges from a trashcan wearing camouflage paint on his face in a reference to Apocalypse Now.
*Read a more detailed summary for this episode on Wiki Simpsons