gringo's arse
This is an uncomfortable ailment that occurs between the buttock cheeks.  This malady is caused by excessive sweat between the cheeks and the friction of them rubbing together leading to a chapped backside.  It is often due to a long bike ride on a particularly hot day.  Gringo's arse is usually accompanied by Foy smell.
Nah man! Theres no way I'm gannin oot for a walk today, I've got a canny dose of gringo's arse!