Why would a person constantly brag (in a joking way) about how attractive they are?

My step-bro (25M) always seems to comment on other peoples' looks. He said that a random girl stranger (who was minding her own business) "looks like a tramp" and was criticising her and her boyfriends' appearance and nitpicking them. But the funny thing is, he always jokes about being attractive himself. He goes "I'm one of those beautiful people. I look just like Brad Pitt" in the company of others. When we talk about an attractive celebrity, he jokes that he is just as good looking as them. Is he insecure or is it something else that makes him act like that?

Why would a person constantly brag (in a joking way) about how attractive they are?
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