"Someone Needs a Lesson" is one of the side quests available in the game's prologue. In this quest, Coen must confront Vasil, who dislikes him for some reason and picks on him. To start this quest, simply approach Vasyl and he will start running away.
Time Segments: 1
Vasil is picking on me again. I've just about had it.

1. Catch Vasil
I've got to catch Vasil and tell him to piss off.
Chase Vasyl down. When you get close enough, a prompt will appear allowing you to stop him and talk. You'll be given several dialogue choices - those marked with a fist icon will force you into a fistfight with Vasil.

2. (Optional) Defeat Vasil
Vasil won't listen to me - so I'll use a different method of persuasion.
If you choose any of the dialogue options marked with a fist icon during the conversation with Vasil, you will have to fight him in a fistfight.

3. Deal with Vasil (1 Time Segment)
Vasil keeps pestering me - again. Maybe it's time I taught him a lesson?
Regardless of whether you and Vasil get into a fight or talk things out peacefully, your confrontation will be interrupted by the arrival of Vasil's father - Atanas. He will be very strict with his son, wanting to punish him and asking you to carry out the sentence.

How you handle the rest of the conversation will determine what happens next. If you listen to what Atanas tells you, you will have to whip Vasyl. If you refuse at a certain point, Atanas will enforce the punishment himself. And if you anger him too much, Atanas will decide to teach you a lesson and attack you.
4. (Optional) Defeat Atanas
Atanas doesn't take no for an answer! I need to defend myself.
If you anger Atanas by refusing to follow his orders, you will have to fight him in a fistfight.

5. Endings
At the end, you'll meet with Vasyl one more time. He'll tell you about the problems with his father, after which this quest will end. Reward: 250XP

Now I know why Vasil acts the way he does - it's the fault of his father, Atanas... Who was likely abused by his own father, and so it goes, generations back.