As a writer (at least, that's the excuse I've been using), I listen to every conversation except the one I'm in. That includes the ones going on in my head. As I said in I Collect People, I am always searching for those unique characters to spin into interesting tales. I also do the same with snippets of conversations that I overhear in malls and small gatherings. Okay, yes I eavesdrop, but people sometimes say the strangest things that would fit perfect into a story. As the saying goes, “Writers are really spies.” The key, however, is to not laugh at the conversation and alert them that you’re listening. Furthermore, you can't let the people you're supposed to be listening to know that you've given up on their conversation, either. That would be rude.