In Penn's math department, there is a "Pizza Seminar". It is on Fridays at noon, only graduate students in the math department are allowed to come, and there is free pizza. Each week a graduate student gives a talk that is intended to be accessible to most graduate students; sometimes they focus on some accessible piece of their research, but more often these talks are expository. (Occasionally, maybe three times a term, a professor speaks -- but still only graduate students are allowed to attend the talk.)
If you Google "pizza seminar", most of the results are similar series in math or closely allied fields (physics, computer science). Is there some reason that such a format wouldn't work well in more distant fields, or is this just historical accident?