Why does my brother show his boxers?

My younger brother is always sagging his boxers. He'll often walk around the house shirtless with his waistband and a few inches of his boxers visible. My brother is quite toned for his age with defined abs and pecs and quite a hairy happy trail so all my girl friends are obsessed with him which makes me uncomfortable. One time his sag was so low I could see his bulge. Can I ask him to stop? Why do guys do this?
Why does my brother show his boxers?
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