A harmless drudge (to shamelessly steal from the great Samuel Johnson). Hated by all, feared by none. Used by the professor as a grader, human shield (those students are so pesky), and repository of creative ideas. Seen by the students as a vindictive not-quite-professor who takes out all her bitterness and angst on her students by giving them D's on their papers just for the hell of it, laughing while she does it. The teaching assistant (TA) lives in a fantasy world where the dissertation writes itself, the students don't challenge their grades, and some day her teaching experience will land her a wonderful job as a tenure-track professor where she can order around her own TAs and laugh while she does it.
Sample sentence: "OMG, I hate my TA, she's so lame," said the student.