 There's a scientific reason your sibling is the worst version of themselves during the holidays. Things like sleeping in their childhood room, a familiar sin, or even a sound can trigger subconscious traumatic memories that might make them act like an angsty teen. This phenomenon is called holiday regression and it's a physical response to stress and anxiety when you go home. It may cause your siblings to fall back into old roles or might subconsciously trigger them to become defensive and emotional. If you notice that you're starting to feel like this, take a breather and go for a walk or for some quiet time in your room.