Mostly,when precepts of Bhartiya sanskriti are violated,this phenomenon occurs."Muh kaala karna" can take place at micro or macro level i.e the recipient of "blackened face can either be individual,family,community or nation.In India,scams and scandals are chief ways of "Muh kaala karna"
Daughter: Hey bhagwan!It was my friend,Deepa..She's cut her hair recently
Hindi Journalist; Congress MP Abhishek Singhvi ke sex tape ne Congress ka Muh kal karn diya. (Congress MP's sex tape has brought disgrace to the party)
Viewer: Aur Kala kar diya? (As if there was further scope for disgrace?)
Modi:Coalgate ne desh ka muh kala kiya hain (The coal scam has blackened the nation's face)