there could be several possible reasons why your brother entered the bathroom while you were in there:
Accidental intrusion: It's possible that your brother didn't realize you were in the bathroom and entered without intending to intrude on your privacy. This could happen if there was a lack of communication or if he thought the bathroom was unoccupied.
Lack of awareness: Sometimes, people might not be as mindful of their surroundings, especially in their own home. Your brother might have been preoccupied with something else and didn't notice that the bathroom was occupied.
Miscommunication: If you didn't lock the bathroom door or give any indication that it was occupied, your brother might have assumed it was available for use.
Urgency: If your brother needed to use the bathroom urgently, he might have decided to enter, hoping you would finish soon.
Playful or teasing behavior: Depending on your relationship with your brother, he might have entered as a joke or to tease you. While this behavior might not always be appropriate, some siblings engage in playful banter like this.
Lack of boundaries: In some households, family members might not strictly adhere to personal space and boundaries, and entering the bathroom while someone else is in there might not be seen as a big deal.
If this situation made you uncomfortable or you value your privacy, it's essential to communicate your feelings with your brother. Let him know that you prefer not to be interrupted when using the bathroom and discuss setting some boundaries and expectations about personal space and privacy in the household. Open and respectful communication can help prevent similar incidents in the future.