This purist - not to say militant - approach to coffee drinking extended to a long list of rules at his brew bar, the Barn Roastery, including a ban on extra milk, spoons, laptops, dogs, mobile-phone ringtones, loud phone calls and ''media'' (apart from newspapers). Sugar is discouraged.
But the rule that has provoked the most heated reaction is Mr Ruller's decision to prohibit pushchairs and prams. ''Coffee Nazis, choke on this swill'' and ''totalitarian coffee regime'' are just two of the many messages of protest Mr Ruller received after he installed a stone bollard - complete with a picture of a pram with a red line through it - in the doorway of his coffee house in the northern Berlin district of Prenzlauer Berg. (The bollard is moved for wheelchairs.)