Learn English – word(s) to describe someone judge others by one tiny detail

I wonder if there is a word or a few words or phases that describe a person very often:

• judge a person based on one or two tiny details or critise harshly over small mistakes that one made (probably by accident)

• ignore the reason behind the details or the mistakes

• often use exaggeration and have twisted logic

For example, one employee has always been punctual but 5 minutes late for one meeting because he was in a car accident. The boss forgot about all the times that the employee was on time and criticized him as 'worthless', 'looser' (exagerated criticising) and refused to listen to any explanation.

Being late was the fact, but the boss is ____ to judge the employee as a person based on this one incidence.

Thanks for the replies, I think these two are the closest:
'judgmental' (too quick to criticise people); 'nitpicking' (find faults in small details)

EDIT: —- I found that this question is marked as 'duplicate' as 'A single word for someone who is not pleased no matter how hard you try'. The answer to that question is 'implacable', I realize that it does fit well in the 'boss' example, maybe because bosses are often described as pure evil, it is easy to link, but what I was searching for wasn't completely about the evil doing, more about deriving the (often wrong) judgement on your entire personality from one small incidence.

Example:

You were having dinner with some friends. There was tea, you took one sip without noticing the steam, found out that it was too hot, by instinct, you swallowed it with your mouth slightly open, which made a noise that sounded like you slurped (detail/mistake). When you went back, your friends made jokes of you and told everyone that you slurp when you drink. They pointed out that it was because you were born in a small village, so you are 'barbarian', you must slurp a lot before you came to the city (judgement). The fact is that you were born in a village but slurping has nothing to do with it (friends have no logic). The incidence at the dinner was because the tea was hot. Your friends know the tea was hot but still make fun of you (ignore the reason) about your (background, status, family etc.).

These friends may talk to you, help you, but they still think you as 'barbarian' because of one incidence. They also laugh with you at others (in the same way) when they find a new target, so you want to say to your friends:
"Hey, you are ____ / it is ____ to treat people in this way, please stop doing that."