Why is my Sagittarius brother so ******* annoying?

That's a true Sagittarius trait, they're just like that. Sagittarians are the most restless signs in the zodiac. They're playful to a fault, and they're known for saying the 'painful truth' , but on the other hand, people know that they can trust what they say because they always say what's real. Sagittarians never hide anything, they're too blunt. They have a great sense of humor. So, when they bug you and making jokes, just laugh at them, I'm sure they'll be happy. These people are very young at heart.