The speaker is fed up, and the poem makes no effort to hide it. Every stanza opens and closes with the same blunt phrase, "screw her" or "screw them," so the anger feels like it's circling back on itself, the way a frustrated thought does when you can't shake it.
The complaints are specific enough to feel real. "Her" seems to be someone who criticizes the speaker, calls them a bad student, and makes them feel guilty. "Them" are people who treat the speaker's body and life as if they had a say in it, judging and holding them back. The poem doesn't say who these people are, which lets the feeling stay central.
The mood is raw and defiant, but there's tiredness underneath. The final line, broken up as "screw. them. all.", reads like someone slamming a door, each word hitting separately. It sounds less like confidence than like a person pushed to their limit, finally saying what they've held in.