It usually means that the person is in a very awkward or bad situation, often by some action (or inaction) on their own part. "I slept late and missed the test. I'm so screwed!" If a person has been cheeted or treated badly, the more likely way to say it would be: "I have been screwed!" It seems like a small difference, but there is definitely a difference in how the two statements would be understood.

screw / screwed - a bad situation; messed up; violated; vandalized; ruined

Yes Biko, I agree with your post.

Usually refers to when a person realises that they have been treated badly, or cheated, that they will say "I have been so screwed"