Any time that one is in an environment where survival is possible without a shirt, the removal of the shirt is highly recommended. Should one be in an environment where acquiring a tan is physically possible, it is imperative that the shirt is removed.
Bro #1: "Dude, I think the sun is about to poke through the clouds!" (Bro removes his shirt)
Bro#2: "Dude, it's 52 degrees"
Bro #1: "Speeder Rule
Bro #2: (removes shirt)