What's it called when you unfairly wrong someone just because you don't like them?
For example: if a teacher marks a students work down just because they don't like the student. Or if a McDonald's worker only fills your coffee cup half way because they remember the last time when you complained about your chips being cold.
I'm not even sure there is a word for the way that person is behaving - 'Stop being so _____?'.
I want to say jealous/revenge/karma/awkward/mean but those words just don't seem to fit. Thank you for your help.
Solution 1:
...because they remember the last time...
out of grudge
A persistent feeling of ill will or resentment resulting from a past insult or injury:
I’ve never been one to hold a grudge
EDIT: As JR points out, 'out of grudge' isn't a very common phrase. (A paltry 1500 hits on Google books)
... just because they don't like the student...
out of spite
A desire to hurt, annoy, or offend someone:
he’d think I was saying it out of spite
Stop being so spiteful
Solution 2:
Resentful
feeling or expressing bitterness or indignation at having been treated unfairly.
Indignant
feeling or showing anger or annoyance at what is perceived as unfair treatment.
Vindictive/vengeful
having or showing a strong or unreasoning desire for revenge.
Solution 3:
Petty or mean-spirited also work here, if the offense is relatively minor (a police officer planting drugs on a suspect because she didn't like his T-shirt slogan would not be petty- it would be criminal).
Solution 4:
When your negative feelings affect your treatment of someone, it is often called "prejudicial treatment". The opposite of this would be "preferential treatment".
Solution 5:
This question admits of more than one answer.
If you are unfair, or do harm to someone just because you don't like them (the teacher example), you can be "morally evil", "unjust", "foul", "spiteful", or a dozen synonyms depending on what you've done.
If you don't like the person because of a minor incident, you are the kind of person who nurses a grievance or holds a grudge (as already mentioned by Tushar).
But for something more serious, and you want to get even, I would say it's revenge. And you may be a revengeful person.
evil (adj) morally bad, causing harm or injury to someone MW
revengeful - (adj) "full of or prone to revenge" MW
grievance - (noun) " a feeling of resentment or injustice at having been unfairly treated" e.g. In the petition, the students listed their many grievances against the university administration. TFD
get even (verb) informal, "if you get even with someone who has done something bad to you, you do something bad to them" TFD
grudge - (noun) " A persistent feeling of ill will or resentment resulting from a past insult or injury" e.g. She held a grudge against her former boss. ODO