The trait, which Beowulf is proudest of when he talks about himself is his BRAVERY.
Beowulf was an hero, who faced and defeated three formidable enemies, that is, Grendel, who was a monster descended from Cain, Grendel's mother and a dragon, which spit fire out of his mouth. Beowulf was a very strong man in his youth and he showed unusual courage in confronting his enemies. He also showed deep wisdom in his old age. He was very proud of his bravery and courage.