Always it means "what a mess!" When somebody said something and then you says "什么乱七八糟的". It means "nonsense" or"I don't know what you say ".

就是很乱很乱的意思。“mess”“messy”可以形容吧！“什么乱七八糟的”包含“抱怨”的意味。He may be complaning if he say so.

乱七八糟 luàn​qī​bā​zāo​ everything in disorder (idiom); in a hideous mess / at sixes and sevens

Means very messy

It means " be in a mess" or messy