“Oh, wow! You are so special. I could never be a stepmom.” I recoil and mutter some kind of response before walking away. It's another one of those awkward social situations in which someone who struggles to connect with people who aren't exactly like they are, ends up giving one of those compliments for moms that aren't actually compliments. In this case, I think her words were maybe meant to be a compliment. However, it's hard to interpret something as a compliment when it's phrased in a way that makes you feel like even their words are trying to hold you and your life out at arm’s length; like there's some part of your existence that smells so bad, other people admire you for your ability to withstand the stench, but they don't want to get too close.
(Pro-tip: “I could never” isnot part of a compliment. It's just not. It sounds like you think their life — which they may love and feel so grateful for and proud of — must be terrible. Like the life they've built is an ordeal to survive, not a worthwhile experience. If you can't relate to what someone else is going through, don't comment on whether you think you could do something you don't understand. It won't feel like a compliment. It will feel like you're looking down on them from the safe distance of your allegedly superior life.)
Sometimes, a non-compliment giver earnestly means to say something affirming, and it just comes out wrong. Sometimes the giver is well-practiced in the art of backhanded compliments, and uses them as a shield to deflect their own insecurities and resentments onto other people. Most non-compliments are reflections of all the weird lessons we've all learned from growing up in a messed up society.
However, whether we say something in response, or just quietly file the information away (“And now I know I should try to avoid So-and-So when I'm feeling crummy about how I look”), just know that while non-compliments like the following can sting (particularly when they unexpectedly fall out of the mouths of people you're close to), you don't have to take them personally. They're really not about you.