Which part of "I'm not interested" don't you understand?

So, I was meeting a friend for drinks before dinner, and she was running late. I thought I was loud enough when I told the bartender I was waiting for someone. This guy, who apparently had been at the bar by himself for a while, decided to chat me up (cue eye roll), so I played the game of "balancing being courteous and keeping my distance."

We went to a known dyke bar after dinner (my friend IS lesbian, but she's not in the market), and she got chatted up by this guy old enough to be her grandfather (cue eye roll, again). The Southern girl she is, she tried to be polite, but he asked way too many questions and she couldn't help being honest. She didn't know how to tell him to mind his own business. Even the other old guy next to him (I don't think they know each other) gave me a knowing look like, yeah, he's so not getting it.

Here's the deal. The first place is a pub, not a singles bar. People usually go with friends to a pub to hang out. The second one is known to be a lesbian bar, so, guys, don't even bother. Really. Going to a dyke bar to pick up chicks has got to be one of the most moronic things men can do.

So, reader, I am asking for your stories. Have you been in a situation where you've gotten it totally wrong? How did you save yourself from embarrassment? Or, have you been in a social situation where you think, this guy/gal/person has gotten it really wrong? Did you try to save them from embarrassing themselves even further, or did you just let them be?

As always, please keep it civil and relevant. I promise I will refrain from commenting on your experience, but I might be curious enough to ask questions to better understand your story.