The thing was, you were never sure whether he was trolling you or not. At a party or some event, supposedly somebody asked him what his research interest was. They were probably expecting to hear something like knot theory or PDE or whatever, but his research interest was "Mathematics", which I guess makes sense because that's what he worked on.
He liked teaching undergraduates but the department only let him do it once every four years or so, as the memories faded from the last time he did it. The year he taught the honors analysis class, it started in the fall with something like 32 students (and all of them by invitation at that) and ended with 6. And so the six survivors printed up T-shirts for having completed the course and wore them to the spring semester final. He's handing out the final and sees the shirts and says something like, "Don't be too confident about that."