Etiquette is a matter of correct form, whereas manners involve considering the feelings of others. A man who holds his knife and fork incorrectly commits a breach of etiquette, while those who sneer at him for it exhibit bad manners. The distinction between manners and etiquette is central to the play.

While Eliza is taking a bath in act 2, Mrs. Pearce returns to warn Higgins that he will have to alter his own behavior if he is to set a good example for his new pupil. Higgins is prone to cursing at the slightest provocation, and his personal habits, such as wiping his fingers on his dressing gown, leave much to be desired.

Higgins has been well brought-up. His mother is a lady who has elegance, good taste, and irreproachable manners. However, though Higgins knows the correct way to behave, he is often too impatient and preoccupied with other matters to pay attention to his conduct or to the effect that he creates in polite society. Both his manners and his etiquette are at fault, but he is aware of the latter when he makes the effort to remember it. His manners are bad because he is self-centered. This is why Eliza says that if she had only had the example of Higgins before her, she would never have learned to be a lady. Higgins retorts that it is not important how one treats people as long as one treats them all the same. He tells Eliza,

The great secret, Eliza, is not having bad manners or good manners or any other particular sort of manners, but having the same manner for all human souls: in short, behaving as if you were in Heaven, where there are no third-class carriages, and one soul is as good as another.

Eliza, however, dismisses this as preaching.

The debate about what it means to have good manners and the connection between manners and etiquette are both important themes in the play. Higgins teaches Eliza etiquette, which is correct form, but he cannot teach her manners, since good manners involve caring about the feelings of others, as Colonel Pickering and Mrs. Higgins do. It is only when Eliza has learned to speak like a lady that Higgins shows any interest in her as a human being, which suggests that his claim to treat everyone equally is not well-founded. The etiquette of others has an effect on him, whether he admits it or not.