Pub Cum is the sticky residue that you normally find on your forearms after a busy shift at the pub. It usually happens when you pass a pint under the guinness tap and it drips a globule of said beverage.
It is commonly used amoung shrewsbury bar staff so it can also be know as a shrewsburyism
Jo: Hey Rob how was your shift at the pub
Jo: Ewwww whats that sticky stuff on your arm
Rob: Ah bollocks Im covered in pub cum again.