Sixtyseven is a bitch

In Circe Ulysses, one reads:

He's getting his pleasure. You won't get a virgin in the flash houses. Ten shillings. Don't be all night before the polis in plain clothes sees us. Sixtyseven is a bitch.

"Sixtyseven is a bitch". What could it mean? I found a brilliant analysis of what it could possibly mean. Some explanations are pretty obscure, others boringly trivial.

I asked a boy, he replied: "Six seveeeeen!".