To sweat profusely, so named after a famous Welsh hockey player of that name who suffered from an extreme perspiration issue - i.e. he just couldn't stop. The origins of this date back to a time, when under the influence of Ephedra, the so-named taff passed out on a subway train following an extreme work out session and copious electrolyte loss through perspiration. To sweat precipitiously is known as 'having a Yandle on'
"Holy Shit James, you have got a right Yandle on!"