Jason was in the same car with his father in-law outside the estate, after a full day with him making it up to his daughter for having been the one to issue the order to let her go to the party.
He was the only person left, Marilyn had left after giving her father the initiative that they weren't on good terms, and he's sure that it's not going to be long before her father starts to preach to him, about the necessity to keep his daughter happy.
Jason was sick and tired of following him around like an underdog. He was tired of having to pretend that he likes him, he has had enough with putting up with his attitude, at reminding him at every point that he's not the one who he had intended for his daughter in the first place.