For example, I overheard a conversation between two coworkers. One asked about a health issue and the other responded with this long drawn out story about an extremely gruesome injury with lots of details leaving everyone extremely uncomfortable. The other coworker complained about to me afterwards, because I overheard it.
He could have said "oh, I'm doing much better! Had a bad injury about six months ago that set me back some, but I'm healed up from that now, thankfully!"
Maybe there's a time and place to share the gruesome details, depending on who your friends are, but it's certainly not with a work acquaintance.
I also question the validity of the cultural concept of "oversharing" being as always bad. Maybe it's bad by definition, but then what is "oversharing?" If you share am I allowed to give you advice?
i'd also say that if someone you consider a friend turns away because of your oversharing, then they probably weren't a good friend to begin with. the only danger is if you tell someone something personal that they end up sharing with others, but that's a breach of trust by that person, not bad oversharing.