Why does Chubukov think it is a burden to be a father of a grown up girl?
Bcz Natalya was fighting with Lomov for petty matters as she didn't know tat Lomov had come to propose her. Again after knowing also she fights. When Chubukov solves the problem and says to Lomov that Natalya accepts your proposal. It was a very tough time for Chubukov to convince Natalya. So he says that it is difficult to be a father of a grownup girl.
Both Natalya and Chubikov hurl abuses at Lomov and drive him out of the house.However Chubukov later reveals to Natalya that Lomov actually cam with the intention of proposing to her.On hearing this Natalya gets frantic and as she is desperate to get married,she forces her father to call Lomov back.This seemed pretty disrespectful to Chubukov as not so long back he had misbehaved with him.However,being an affectionate father,he couldn't decline Natalya's request and had to go through the humiliation of calling Lomov back.Hence he feels that it was a huge burden to be the father of a grown up daughter as she kept blowing hot and cold as it suits.