Cockiness is the noun for that too-sure, showing-off confidence that annoys people. If cockily is how you act, cockiness is the quality you have. It is informal and a little criticising. Coaches, teachers, and friends use it when someone thinks they already know everything. Though actually it is not as heavy as arrogance: cockiness often still feels young and bouncy, like a teenager showing off, not like cold pride from someone in power. A little confidence is fine; cockiness is when you stop listening.