accidents
Explanation
The Joke
A woman tries to comfort someone by saying "It's okay, sweetie. Everybody has accidents sometimes." A man standing nearby immediately responds "Not me." The woman turns to him, annoyed: "Honey..." She then tries a different approach: "Wait, if you're so perfect, if I'm wrong, give an example." The man considers this, and says "But I don't believe I'm self-aware." The woman's retort is devastating: "Then have you ever been in an accident?" -- implying that he himself was an accident (i.e., an unplanned pregnancy).
The comic starts with a familiar domestic scene -- a parent reassuring a child who has had an accident (likely a bathroom accident, given the context). The father's smug interjection that he never has accidents sets up the punchline. His claim of perfection backfires when his wife implies that his very existence was an "accident" -- that is, he was an unplanned child.
The Humor
The humor works through a classic bait-and-switch on the word "accident." The setup leads the reader to think about the everyday meaning (spills, mistakes, bathroom mishaps), but the punchline pivots to the euphemistic meaning of "accident" as an unplanned pregnancy. The husband's arrogance in claiming he never has accidents ironically sets up the insult perfectly. There is additional humor in the middle panel where he claims he is not self-aware -- a statement that is both philosophically interesting and also, in the colloquial sense, very accurate about someone who would brag about never making mistakes in front of his embarrassed child.