A few days ago, an existing Fortnite account owner changed their username from something totally unrelated to littlestjeff1, following the revelation of littlestjeff1 as a name on YouTube.
You wouldn't even be able to change your username to littlestjeff1, given that the original account would have to be changed or deleted itself to free up the username.
Epic is claiming this:
You wouldn't even be able to change your username to littlestjeff1, given that the original account would have to be changed or deleted itself to free up the username.
As far as I know, they haven't disclosed the status of the original account (which may have been deleted?).