I wrote about that film here.
In that film Flavio Bucci sports thick glasses and plays the part of a nerdy sociologist who takes notes of the audience’s reactions during the screening of the film.
Afterwards he is interrogated by the police. Has he seen anything which can solve the murder of a man in the audience by a gun man IN the film?
You can see Mr. Bucci from 27:20 onwards.
Mr. Bucci also played in the sex comedy Gegè Bellavita (1978) which can be found in full on YouTube.