You blackened my face...

Another installment in the literal illustrations of Arabic slang.
"Sawadtilli wijji" means, literally, "you blackened my face". In context, it means you've embarrassed someone, or brought them shame (which we all know is a sin in Arab culture... Punishable by death - that actually isn't even an exaggeration)

Personally I couldn't care less if you blackened my face. I'd just throw some back at you.