I'd be sitting on the second floor doing my programming assignment late at night on a weekend, and he'd just wander by, stop for a moment, look at me, then continue pacing. Or he'd be outside smoking when I left XD..... And sleeping on chairs around campus. For a while I thought he was homeless, since I'd see him sleeping in his office or the library and wearing the same clothes for a few days, but I think he just really considers the campus to be his home.
I had Tom for Multi-Dimensional Calculus at UNH a few years ago. I slept through my final and he let me take it later that day without penalty. Front page worthy professor.