What, just out of the blue? You, like, walk together with someone consistently defensive and all of a sudden they go “Don’t treat me this way!” Everyone is dumbfounded.

No, of course not. Being consistently defensive only comes from being consistently attacked, it’s only logical. The attack may not be coming from you, sure, but don’t underappreciate how often people attack each other unconsciously. Pretty much all the time. All kinds of judgments. So the person who is always defensive is sick of that and he sees attacks everywhere. He is not entirely wrong to. Maybe what you said was not meant to be an attack, and maybe it wasn’t at all, even unconsciously. Maybe it was completely innocent and pure. In that case, if the person becomes defensive, it should not be hard for you to calmly and kindly explain that you did not mean it the way they took it, apologize and be genuine about it - that’s the best you can do, the rest is up to them. If, instead, you tell them how defensive they are, how sensitive they are, or that they tend to take everything personally, this is, of course, another attack. It won’t help one bit. How can you break through someone’s defensiveness by accusing them of their defensiveness?