Bigger than Barbie Footballs

I told Jed my next post would be about the biggest grapes I'd ever seen. Really big grapes, about three or four times the size of regular grapes. I can't get the metaphor. Smaller than eggs, bigger than Barbie footballs.

Loni* my coworker had these grapes in a ziploc bag, and she was sharing them with the office. Radioactive, I said. Steroids, Uncle F. said.

There was laughter. They were pretty good, sweet green grapes.

Nothing makes Loni happier than putting something really big in her mouth, Molly said.
Molly is very funny. I have a file going with her lines.

Now, I can use this bit in a story I happen to be working on, although grapes won't work, since the piece is set in a bar. But I was wondering how others handle overheard dialogue, especially if it's good. Is it stealing? Do you ever use it verbatim? Do you save it until you have a story it will fit into? Or do you work it into whatever you're writing, so you don't lose it?

What about other little observations and details? Do you come up with them to serve your story, or do you see the actual thing first and then somehow work it in, give it to a character, build a scene or story around the real moment?

Sometimes I think part of my problem is that I do it backwards. I often start with details and have no idea what the main plot of my story is about...

I'm also wondering where Jed has been. I haven't heard from him since I typed, okay, you be the husband, in the IM window....

*all names have been changed to protect the innocent.