Yes, this is a good question to ask.

If the person you are asking is really *found of testing* he would be very exited to tell you the story. It does not matter whether he is a manual tester or automation engineer, **the one should have something to be proud of** (but we should consider that he is telling the story from his point of view, I mean this bug could be not that impressive for a Automation Engineer but a kind of great bug among Manual Testers team)

And here is my example: **memory leak defect**.

When I had just been employed there was a problem in software: sometimes it crashed in unpredictable manner (sometimes during one action, sometimes during another action). At that moment I was testing mainly with QTP (now UFT) and started to try Java-tests. The advantage was great: I could check JVM-memory during execution and dump memory usage right at the crash time (with MemoryAnalyzer-1.6.0). After analyzing memory it was clear that there were 8 object that were duplicated many times during program execution. So I reported defect with certain object names. Devs liked that because it was supposed before that there is nothing to do with this unpredictable crashes and localization of the bug was of a top level.