It is wrong to physically assault your partner's friends.
Irvine is being insulted by his friend Mike's friend.
Irvine wants the insults to stop.
Irvine walks away from the situation without saying anything.
Irvine punches Mike's friend in the face, so he'll be quiet.
The situation is defused without anyone fighting anyone.
Mike gets angry and assaults Irvine in retaliation.