I told a girl in the library to stop hogging the seat
Was she actually being inconsiderate?
No, I'm just angry and I want to ruin her studying day.
Don't make others suffer for your bad moods. I imagine you wouldn't want someone doing that to you.
I'm upset, I just want to shit on her day.
But treating other people badly is not going to improve your mood, it will just make people around you angry and critical, which would just make your own day even more difficult. If you are angry and irritable, it might be best to just go back home, or find somewhere to be alone.