For some reason, satan put siblings on this earth to ruin our lives. Even if you deeply love your siblings, it's par for the course to have a couple stories of them embarrassing you in front of a romantic partner. After all, what's the point of surviving growing pains together if you can't humiliate your sister in front of her partner with some facts about her younger years?!
At the end of the day, most (non-abusive) sibling humiliation is harmless, and acts as nothing more than an annoying love language. However, there are always exceptions, and digging up a sibling's dirty laundry in front of their partner can transcend regular embarrassment and enter a whole new realm of hell.
"AITA for kicking out my brother, who our parents have previously disowned, because he told my (now ex) fiancé that I cheated 9 years ago?"