Being There (1979) Peter Sellers, Shirley MacLaine

Simple-minded Chance, a gardener who has resided in the townhouse of his wealthy employer for his entire life and been educated only by television, is forced to vacate his home when his boss dies. While wandering the streets, he encounters business mogul, who assumes Chance to be a fellow upper-class gentleman. Soon Chance is ushered into high society, and his unaffected gardening wisdom makes him the talk of the town.