literally like tofu strung on a horsetail which is impossible to lift; used to describe a situation or object too weak or poorly constructed to be supported

这个烂摊子就像马尾穿豆腐，提不起来。

figuratively used to say 'don't mention it' or 'let's not talk about this', based on a pun on the word 'ti' (meaning both to lift and to mention)

过去那些丢人的事，真是马尾穿豆腐，提不起来。