Being on ones-own. Shorter form of playground jibe 'Billy Bates, got no mates'. Referring to some imaginary character 'Billy Bates', who is too sad to have any friends.
Can refer to ones-self as 'being on my bates'. In other regions is just referred to as being 'Billy No Mates
Example1: Look at Malcolm is playing on his own, arrrr, he's Billy Bates, got no mates!
Example2: I'll order a pizza tonight, I'm on my bates.