It seems strange to me that this is the kind of family news you choose to broadcast over the Internet.

(There may be some backstory or context that I’m missing.)
Many women like to be flirted with or know that men find them attractive, especially as they get older (they like to know they’ve “still got it.”) Even if it wasn’t the case at all that this man was “checking her out”, and your mom really likes to get attention by telling these stories, this seems like such a minor thing. If you can ignore it, I would think the prevalence of these kinds of things would lessen (I’m imagining that since you posted about it, it must be somewhat habitual.)
I’m also thinking that your mom may have some kind of self-confidence issues. My sister, who is young and very attractive, constantly goes on and on about how she has so many boys who like her and how she just can’t choose among them. But she’s really very lonely and has very poor self-esteem - she thinks her attractiveness is the only thing she’s got going. It is really annoying to have to listen to, but when I am talking with her and she starts in on this kind of thing, I try to steer her toward acknowledging other qualities she has that are more important. Less annoying for me, and hopefully confidence building for her. It also sets an important boundary. If she insists on the “I’m so great because I’m pretty and I have all these boys” topic, I suddenly have to hang up or do something else. I’m not rejecting her, just the endless dwelling on the topic. I also make sure that she knows that I think there’s more to her than that. I don’t tear her down more because she can be annoying on occasion.
So, for an example of how this can work:
JLC’s Mom: “Did you see how so and so was looking at me? I didn’t have my wedding band so he must have thought it was his lucky day!”
JLC: “You do look really good, Mom. [affirmation] You always take such good care of yourself. [starting to steer to more important topic] That reminds me - can you tell me where you found that recipe/bought that outfit/what the name of that book you were reading [topic choices - endless]?”
Your mom can either go with the topic or if she chooses to insist on the other one, you can leave:
JLC: Look, Mom, I really have to go, but if you remember [your chosen topic], please let me know!
And then you hang up or leave the room or whatever.