die Ruhe weghaben

Perhaps from northwestern German etwas weghaben von (“to have got something from”), also used of inheritance as in: Die langen Ohren hat er von seinem Opa weg. (“He has inherited those long ears from his grandad.”)

die Ruhe weghaben

1. (colloquial, idiomatic) to be very calm, especially in situations where others would not be; may be used positively, but also negatively, then implying lack of interest, tardiness

   Synonym: die Ruhe selbst sein

   Normalerweise sag ich immer, man soll sich ’n Taxi nehmen, wenn die Frau in den Wehen liegt. Aber beim Peter hatt’ ich da keine Bedenken – der hat ja die Ruhe weg.

   Generally I always say you should take a taxi when your wife is in labour. But with Peter I had no worries – he's cool as a cucumber.