Funny, I was at a birthday party the other day and had the same thoughts.
There was an HB8 that was friend of a friend-that never met me, but wanted to meet me (I won't get into the story of how this came about). We talked for maybe 5 minutes at this party, and it was ok-don't think I did a great job, but made good eye contact, was ****y, etc.
Anyway, when I got to the party, which was at a bar open to the public, she had been talking to two guys. One was following her around the entire time, and to my knowledge, was someone who was not with the "party" but someone she'd met at the bar.
The guy was following her around the bar like a puppy, it was pretty pathetic. The funny part is, I caught her looking at me twice (after she'd run off from our conversation and didn't come back), when I was talking to a girl I've known for a while. The girl I was talking to had b/f, it was just friendly chat, but the HB8 is new to the circle, so I am sure she didn't know that (a little social proof at work maybe?)
Anyway, her body language as she moved around the bar, compared to his inferior body language, was very obvious to me. And 5-10 years ago, she was probably an HB9, so I have no doubt she probably falls into the category of woman that this stuff we talk about on her was pretty much written for. Even though this guy was technically competition, I almost wanted to pull him aside and say "Dude, wtf are you doing?" I did point out his behavior to a few AFC friends of mine, and even they-with their limited knowledge-agreed.
I say if it's a friend, then casually mention your observations. If it's not someone you know-as was my case- you're likely just to offend them, so I wouldn't bother.