Having no idea about what they just learn in CS. I've ran into CS majors who barely graduated and pretty much know nothing.
Then there are those who did really well, but all they can do is program in the language they were taught. They struggle learning a different language, or picking up a broader range of programing knowledge and theories.
I see this in a lot of majors, but most people chose the major because they think it will lead to a job. In other words they didn't learn it because they like it, they treat it as if it's training for a future job.
