Our new boss is a strange character. His pet hate (Lieblingshassobjekt) is a messy desk. At the end of each work day, all of our desks must be completely cleared – not a single piece of paper is allowed. At first my colleague was resistant, so our new boss approached his desk at the end of the day and with one big swipe of his arm, sent all his papers to the floor!
An alternative version of this idiom, which is more common in the US than the UK, is pet peeve.