I see a lot of guys with their shirt hitched and tucked in their belt/pants just at the front, revealing their belt buckle and crotch area. I don't think this is unusual.
But guys actually walking around with the bottom of the front of their shirt in their hands and pulled up to show their crotch and lower abdomen is something I can't say i have seen. And if I did I am sure they would look like morons*
*although a moron showing a nice VPL and bulge will be excused!