I'll give an example.
I have a disability and sometimes need a motor cart in the grocery store. Right now I'm nursing an injured knee, so this is one of those times. A few days ago when my husband and I were shopping, I was driving around a tall display of produce when I saw the front end of another motor cart driving around around the other side. We stopped in time to avoid a collision, I backed up and let him pass around first, and he wisecracked, "We've got to stop meeting like this." Naturally I laughed.
I encountered that man a few minutes later, and he said something like "Here we are, meeting again." I joked back, "Yes, and right in front of my husband, too!" Mike hadn't been present during the first encounter, and *just in case* that man had any designs, this was a good way to play along while still making it plain that I have a husband. (The gentleman was also married, it turns out.) We went our separate ways, and I explained the dialog to Mike, who otherwise wouldn't have known what in tarnation that man and I were saying to each other.
For the remainder of that shopping session, every time that man and I passed each other, he made some kind of remark that alluded to a couple having a clandestine meeting. Frankly, after a while it started getting creepy. I know he meant no harm. It just felt a little strange. Not threatening, but in the sense that hey, a joke is only funny the first couple of hundred times, and after that it wears thin.
Was he flirting with me? Probably, since he was definitely making jokes that had a sexual undertone, but he was never trying to "pick me up." Was it wrong or immoral? Depends who you ask. My husband wasn't offended. Would that man's wife have been? Don't know.