Danny de vito
What is he doing with the knife during the first dinner? And when he puts some of the food on his lady friends foot?
shareHe uses the knife to rip open his date's nylons so that he can massage part of her bare foot, specifically her toes. The scene is there to establish that DeVito's character has a foot fetish which Barbara then uses to her advantage later on the film when she tries to seduce him in his office.
I watched the blu-ray with the directors commentary and DeVito admits that it was his idea to rub gravy between her toes.