A man wearing a Hasidic Jew’s black hat is walking. He meets a man wearing two stacked hats of the same dark style. This gives the one-hatted man pause. He then reverses his stride, walking backwards away from the dual-hatted man.
This comic makes marginally more sense if you know that dark Hasidic Jew Hats are a sign of ill intent and malevolent intelligence in the XKCD universe. It suggests that the typically evil black-hatted anti-hero is afraid of someone with even more hats. The author, we assume, does not intend to apply any anti-semitic connotations by this message.