The tweet references an undated incident at an unnamed restaurant in Hamburg, Germany. The tweet narrates a 50 Euro Fine by "man in uniform from a Social Security organisation" imposed for non-consumption of victuals ordered at a restaurant.
I do not deny wastage of food is, at the least, poor practice. But that is digressing.
A google search with the keywords "Germany waste food fine" indicated apparently some restaurants in Switzerland, and the UK apparently levy a penalty on customers who leave food on their plate. Yet a charge levied by a restaurant is a very different proposition from a penalty levied by a Social Service Organisation; the latter would IMHO IANAL mandate a law. Further I'm sceptical that the same penalty was not enforced by the restaurant itself if it was a law.
Is there a law in Germany (or Was - since the earliest reference I find dates to 2011) to penalise a customer at a restaurant for leaving food/drink unconsumed?