Someone who is cocky is so confident and sure of their abilities that they annoy other people. [informal, disapproval]
He was a little bit cocky when he was about 11 because he was winning everything.
Synonyms: overconfident, arrogant, brash, swaggering
cockiness uncountable noun The pair of them were both blinded by their own cockiness.
Synonyms: overconfidence, vanity, arrogance, conceit