Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic plays on the awkwardness of "conception day" -- the logical but uncomfortable implication of birthdays. A family stands at a party wearing party hats, but instead of a birthday cake, they appear to be burning money in a pan alongside broken balloons. One parent asks: "I don't get it. What holiday is celebrated with accidentally broken balloons and burning money?" The caption below provides the "Fun Fact: Nine months before your birthday is your conceptionday."

The joke works on multiple levels. The "accidentally broken balloons" are a reference to failed contraception (broken condoms), and "burning money" refers to the financial costs of an unplanned pregnancy and child-rearing. The party itself is a darkly humorous celebration of the parents' accidental conception of their child, complete with visual symbols of the mishap that started it all. The parents' unhappy expressions reinforce that this "holiday" commemorates an event that was perhaps not entirely planned.