If you gravitate towards off-duty style, why not pair a navy and green horizontal striped crew-neck sweater with white jeans? Rounding off with a pair of dark brown suede desert boots is an easy way to bring some extra fanciness to your outfit. Keep this combination in your front hall wardrobe come warmer weather, and we guarantee you'll save a lot of time getting ready on more than one morning. This combination suggests how to slay in casual dressing as a 20-year-old guy.