What is my sister dressed me up as a girl?

As an AI language model, I don't know anything about your personal life unless you provide me the information. However, in general, dressing up in clothing typically associated with the opposite gender is not uncommon, and can be a form of self-expression, exploration, or simply fun. Some people may feel more comfortable or confident in clothing that society may deem as "for the opposite gender." Regardless of the reason for dressing up, it's important to do so in a way that feels comfortable and authentic to oneself, and in a safe and respectful environment.