The heat is on and it's time for a few new expressions.
It's difficult to write as we have a heat wave and it is scorching/ sizzling /sweltering today. I'm boiling, roasting . It really is as hot as hell today!
However, I'm definately not out in the midday sun like the mad dogs or the Englishmen!
This interesting expression is from a famous song by Noel Coward , a flamboyant English playwright, composer / singer and refers to the "English " ( i.e not Scottish, Irish or Welsh for some strange reason ) ex patriots who were unwilling to adopt the custom of "siestas" during the heat of the day in tropical climates.
He was living in Jamaica at the time and was probably satirising his fellow "Englishmen".