Night Classes

Vuyo: Dumisani, I've been taking night courses for 5 months now and I have an exam next week.
Dumisani: Oh!
Vuyo: For example, do you know who is Graham Bell?
Dumisani: No
Vuyo: He's the inventor of the phone in 1876; if you take
Night courses you would know this.

The next day, the same discussion took place:
Vuyo: Do you know who Alexander Dumas is?
Dumisani: No
Vuyo: He's the author of "The 3 Musketeers", if you take night
courses,you would know this.

The next day, once again:

Vuyo: And do you know who Jean Jacques Rousseau is?
Dumisani: No
Vuyo: He's the author of "Confessions", if you take night
courses, you would know this.

This time, Dumisani got irritated and said: And you do you know who
Is Sipho Magwaza?
Vuyo: No
Dumisani: He's the guy sleeping with your wife. If you stop night
courses, you would know this!!