what-if-i-never-existed
Explanation
The Joke
A person asks the classic existential question: "Do you ever worry the world would be better off if you never existed?" Another character immediately reframes it: "Let us make that question more general. If a random individual never existed, would the world be better or worse?" They reason that this is pretty clearly a 50-50 proposition -- unless you have some reason to think you are not a statistically random individual, the question practically answers itself.
The first character, deflated, says "I was originally asking for sympathy in a moment," and the other replies, "Well, you phrased it in a dumb way." The comic takes what was meant as an emotional, vulnerable confession and subjects it to cold statistical logic.
The Humor
The humor comes from the clash between emotional vulnerability and ruthless analytical thinking. The first character is having an existential crisis and fishing for reassurance, but instead gets a probability lecture that, while technically valid, completely misses the emotional point. The response is mathematically sound -- if you randomly removed any person from history, there is no particular reason to think the world would be systematically better -- but it is also the least comforting possible way to address someone's insecurity. It satirizes the kind of person (common in SMBC's nerd audience) who responds to emotional situations with logic puzzles.
The votey shows someone saying "Also, your hair sucks" -- adding a gratuitous personal insult on top of the already unsympathetic response, making the interaction even more hilariously unhelpful.