Tokyu Corporation interview questions

the interview process generally was fine. i got to go through 4 selection rounds. the interview questions were easy. they had agreed to offer me this job. However, things started getting ridiculous when we negotiated about the starting date. Due to some private plans that i had scheduled, I generally asked them to either move the starting date 1 week earlier or 1 week later. Be advised that, they were not in rush to fill up this position as I asked the headhunt before, and I thought there was a room to negotiate for the starting date. Nevertheless, the line manager got mad at me and threatened to withdraw the offer if I didn't write the apologize letter for "being dare to negotiate the date with them" . this is such ridiculous!! if I were given another chance, I would never ever applied for this company again.