One of the first lessons any teacher learns is that they’re always biased.  This is actually true.  Teachers are biased, just like anyone else.  However, students take it one step further into assuming the teacher is always biased against them personally.  This is far, far less true.  Still, everyone has had that teacher they assumed personally hated them, so it makes for a good joke.

By the way, that teacher did hate you.  They told me so.