On the introduction day of my Computer science course, we all were to sit in "welcome groups" and tell a little bit about our programming background.
Most of us were beginners, but one of the guys told me he'd been "messing around with some Java a while back", so I thought I'd ask him about help when we had our first real Java programming assignment. I was surprised to learn that he wasn't able to help me at all. He seemed to know less than me, a complete beginner, on the different OO concepts and Java syntax. Furthermore, he seemed to have zero interest in anything development related.

It was later revealed that he meant that he had been messing around with INSTALLING Java on his computer a while back, but never really made it work. *facepalm*

Needless to say, he was a great group member in the assignments that followed. /s