Cloud Burn is the process of the magnification of the sun through clouds making it easier for your skin to burn. It sneaks up on you like a rash...
At Download Festival:
Twat "Hey... the clouds are out... I won't burn"
Rooster "Yeah you will... cloud burn!"
**2 hours later**
Twat: "Man I wish I had lotion, a poncho or something because shit I'm burnt.