spacial has a point
Personally, I do plan on getting a tattoo on my chest, but it's not going to even touch any chest surgery scars and will be on my chest simply because that's how it popped into my head and that is where it would look best I think.
Just because someone asks a question doesn't mean you have to answer. I have been asked about scars before, but only when they were still in the injury category: after that, never. Injuries are asked about far more often than scars -- far more often. Even with a scar you don't have to answer, and if you do a simple answer will do if you care to entertain. If they ask further (I.e. What kind of surgery) just tell them to mind their business one way or another because unless they're a good friend (and sometimes even then) that's just rude. Some people even offer up outlandish, obviously ridiculous stories in response whether to make it more interesting or as a way to tell them it's none of their business: regardless of their reason it usually puts a stop to any more questions.