Out with friends this morning. Hot but cloudy. I covered mine in suncream and offered it to friend as she had commented that she didn’t have any.
She refused and said her dc didn’t need it anyway as it was cloudy and didn’t believe me when I said you can still burn on a cloudy day! 
I really think they should teach this in schools (maybe they do these days but certainly didn’t when I was at school in the 1990s).
YABU: everyone knows you can still burn on a cloudy day
YANBU: I didn’t know you could burn on a cloudy day