Uniqueness
Explanation
The Joke
In the first panel, a woman enthusiastically says, "Isn't it amazing how every snowflake is different from every other?" and a man responds, "Sure." She then adds, "Also, isn't it amazing how each pile of dog poop is unique?" In the final panel, the man says, "Nobody likes a miserable asshole," and the woman counters, "Did you know that every anus is different from every other?"
The Humor
The comic deflates the cliche inspirational observation that "every snowflake is unique" by pointing out that uniqueness is not inherently special or beautiful -- every pile of dog poop is also unique, as is every anus. The woman keeps applying the same logic of marveling at uniqueness to increasingly unpleasant things, showing that uniqueness by itself is a trivially true property of most complex objects and not a reason for wonder. When the man calls her a "miserable asshole," she treats even the insult as another opportunity to make her point about the uniqueness of anuses, refusing to break character.