At the end of Scene 3, Hamlet appears to insult Claudius by calling him "my mother." Claudius, characteristically, conceals any anger he might feel, no doubt thinking that Hamlet will understand his true feelings when he is having his head chopped off in England.
But, come, for England! Farewell, dear mother.
Thy loving father, Hamlet.
My mother. Father and mother is man and wife. Man and wife is one flesh - and so: my mother.
Some of Hamlet's zany behavior and utterances are amusing, but it is hard to see why he would think it was witty or amusing to call Claudius his mother. He can only be doing it to keep up the pretence of being crazy. Claudius, however, is no fool. He is likely to understand that this is not madness but pretense. He doesn't really care much, now that he thinks he is getting rid of his number-one problem. It is interesting that both Hamlet and Claudius are acting.