1. The "person" who wants the name is a fictitious person, not an actual human individual who deserves consideration as a human being. There's no point of "being cool" toward a company, it's just out to get what it can: asking for your username is just an example of the ruthless logic under which company's operate.
2. The value to the company is high enough that they have invested time in approaching you and should you decide to give up your name, will invest all the time in actually transferring it.
3. If you do transfer it, don't be surprised if the company sells it or does something equally unexpected. Acquiring the name is a business transaction. Nothing more. Nothing less.
Finally, if you don't care about the name and don't want to be bothered, then let it go so you can do something you care about and are willing to be bothered by.
Good luck.