cock of the roost
An arrogant, conceited, or overly proud person, typically a man. He struts around campus like he's the cock of the roost, all because his dad is some politician. Don't invite Joe to lunch unless you want to hear him brag about all the important things he's doing in his new job. He's just the cock of the roost lately. You're not going to make many friends at your new school if you walk around like the cock of the roost.
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