A person with no friends, or at least someone who appears that way.
Other similar uses:
1) On his bill - On his own
2) Has been billied - Has been abandoned (by friends)
3) A billy
- one with no friends
"That Danny lad is a right billy-no-mates."
"Look at that lad over there on his bill."
"David's been billied! Haha!"
"Ryan is a billy..."
An old irish slag to make fun of one with no friends. If you're irish and happened to be called billy you're a very unfortunate person.
Billy no mates is used in many cruel jokes.
joke: "Why did billy have no mates?"
"He was in a wheelchair."