There is a youtube video of renowned physicist Sidney Coleman (RIP giving a classroom lecture about general relativity or something. I was watching it, listening along, and at one point in the lecture he stopped to light a smoke, then kepc lecturing with the cig in his hand. I almost busted up laughing.

Oppenheimer also would lecture while holding a cigaratte, according to biographies of him that I've read, but he was before my time and I've never seen any videos of him.