What I notice is the crew neck, which has a slight stretch for easy movement.
Reebok Spell Out Logo Sports Athletic Gray Short Sleeve Shirt Men’s Size Large
You will find the crew neck sits at a height that works with most jacket collars.
Reebok Mens Identity 100% Cotton Tee Shirt – Recovery Blue- Medium -Brand NWT!
What stands out about the short sleeve is the reinforced stitching at the seam.
Reebok Mens Identity 100% Cotton Tee Shirt – Very Berry – Medium -Brand NWT!
With short sleeves, you can easily roll them up for an even more casual look.
Reebok Above The Rim Mens L Gray Graphic Print Basketball Cotton Jersey T-Shirt
A nice touch here is the graphic print that uses only two contrasting colors.