It could be that OP is not really doing a good job of explaining. Calling the coworker dumb is a red flag to me. I had an employee who seemed to have trouble r

It could be that OP is not really doing a good job of explaining. Calling the coworker dumb is a red flag to me. I had an employee who seemed to have trouble receiving my guidance. In his case, there were several issues at play, his and mine. Ultimately, I found the level at which I had to interact with him in order to get my message across. I was assuming that he was where I was in the process of rationalizing the solutions I was proposing. What I came to understand is that he didn't take orders well. It just wasn't in him to do so. Instead, he was driven by understanding why we were doing things a certain way. I was frustrated by him and that never went away, but I knew that it was my responsibility to get him to understand.