cocksure

vuorenvarma puhekieltä too confident; overconfident

I thought myself cocksure of the horse which he readily promised me. — Alexander Pope.

The persistence of the Past is one of those tragicomic blessings which each new age denies, coming cocksure on to the stage to mouth its claim to a perfect novelty.

These crack specialists, the young scientific fellows, they're so cocksure and so wrapped up in their laboratories that they miss the human element.