A portmanteau comprised from the expressions
Captain Obvious} and King of the Assclowns, aka [Donald Trump. It is a clever play-on-words and ideas because it demotes Trump from his real-world title of President and Commander-in-
Chief, and his wannabe title of King of the World, to the
rank of a mere captain, and that being inferred as more-stupid than the low-IQ Captain Obvious.