The man is asking who stole his banana. The woman responds with something completely unrelated - therefore breaking the Maxim of Relation. This may be because she is trying to distract the man from the banana skin in her hand.
Here the man asks a direct question. The woman answers with something untrue: Clearly she DOES know what he is talking about. She is therefore breaking the Maxim of Quality, presumably because she doesn't want to admit guilt.
The woman has been caught yellow-handed. The man demands an explanation, but all he gets in return is a 'mneugh!' The woman providing too little information, and thus breaking the Maxim of Quality. The effect is to demonstrate that, after all, she doesn't really care if he knows.