To the young woman at Collins Beach: It was shaping up to be a naked mellow day. My wife and I found some nice open space near the old pilings. You and your friend found good space as well. When we got back from a walk, we saw that guy in jeans lying in the sand right next to your towel. He was watching you while your friend was out on her floaty. I came over to ask you if he was bothering you. I'm pretty sure you said he was.
When I asked him to move, I noticed the metal weapon he had in the sand behind him. I feigned removing a barefoot hazard and picked it up. The ruse did not work and it was quickly apparent that this guy was not real stable when he grabbed it from me. De-escalation was in order and we retreated to our chairs.
After reflection, I asked my wife if I was being a bit too paternalistic. "Maybe. After all, you are a dad." Anyway, sorry to assume you needed help. Hopefully you won't be bothered by me or anyone else next time you come out to the beach.