dad-joke
Explanation
The Joke
A father asks his son, "Hey son, would you like a dad joke?" The son says, "Go ahead, Dad..." The father then screams, "YOU'RE LOOKING AT ONE!" -- meaning he himself is the "dad joke," i.e., a joke of a dad. The comic then cuts to a flashback labeled "EARLIER..." showing the father being fired from his job ("You're fired, Mister Jones"), which provides the context for why he considers himself a joke.
The setup leads the reader to expect a corny pun -- the classic "dad joke" format. Instead, the father turns the concept on its head: rather than telling a dad joke, he declares that he is a dad joke. The flashback reveals his self-deprecation is rooted in the very real humiliation of losing his job, transforming a lighthearted premise into something unexpectedly dark.
The Humor
The comic plays on the double meaning of "dad joke." Normally the phrase refers to the genre of wholesome, groan-worthy puns that fathers are stereotypically fond of. Here, the father reinterprets it literally -- he is a dad, and he is a joke. The sudden tonal shift from playful wordplay to existential self-loathing, reinforced by the reveal that he has just been fired, is a classic SMBC move: taking a familiar, benign concept and steering it into bleakly comic territory. The father's wild-eyed delivery of "YOU'RE LOOKING AT ONE!" sells the desperation.