This combination of a black v-neck t-shirt and blue skinny jeans is proof that a straightforward casual outfit doesn't have to be boring. For something more on the dressier end to finish off this getup, complete your getup with a pair of black leather desert boots. So as you can see, it's a sharp, not to mention season-appropriate, ensemble to have in your transeasonal wardrobe. This ensemble suggests how to slay in the casual style department as a 20-year-old guy.