Roma bene (1971)

Nino Manfredi is a police captain, giving an onlooker's point-of-view towards the decadent society folk. Party itself features a down & out baron, who dances with the party's glamorous hostess Virna Lisi so that he can steal her valuable earrings. When they're missing, she's angry enough to call in the cops (Manfredi shows up) and have the baron taken away.