Lady GaGa is the correct answer because she is the only artist in the given list who is known for her unique and eccentric style, both in terms of her music and her fashion choices. Adele is known for her soulful ballads, Ke$ha is known for her party anthems, Bruno Mars is known for his smooth R&B and pop sound, and Madonna is known for her provocative and boundary-pushing image. Lady GaGa, on the other hand, is known for her avant-garde and theatrical performances, making her the odd one out in this group.