A criticism that is as old as Diogenes (at least Laertius) is that they were essentially a cult of edgelords. They pretended not to care what people thought, but it was just an act, at the same time it was really important to them that people around them knew how little they cared through all the shockingly (lower case) cynical things they said and did. DL has Plato accuse Diogenes of this directly. All this is reducing a philosophy to a trope, but it's not an entirely unfair accusation either.
Speaking of which, a bizarre and entertaining piece of history is Lucian's extremely hostile biography of Peregrinus Proteus.