This pattern is used to say that someone cannot do something well or enough, or that they do something improperly. It often carries a critical or disappointed tone. The phrase ろくに is an adverb that pairs with a negative verb to mean 'not properly' or 'hardly'. It is used when you expect a certain level of quality or quantity, but the reality falls short. For example, if someone hasn't studied at all for an exam, you might say they ろくに勉強しなかった. It can also express that something is barely done, like not eating properly due to being busy. This pattern is common in spoken Japanese, especially in complaints or observations about someone's behavior.