drink
Explanation
The Joke
A man at a party announces a logical paradox as a drinking game rule: "If the following statement is true, I will immediately take a drink: I am not about to take a drink." This creates a self-referential contradiction. If the statement "I am not about to take a drink" is true, then by his rule he must take a drink, which would make the statement false. But if the statement is false (meaning he is about to take a drink), then the condition for drinking is not met (since the statement is not true), so he should not drink, which makes the statement true again. The other partygoers stare at him with visible annoyance and boredom.
The caption reads: "Nobody likes the Bertrand Russell Drinking Game," confirming that bringing formal logic paradoxes to a casual social gathering is a surefire way to kill the mood.
The Humor
The comedy works on two levels. First, there is the inherent absurdity of applying rigorous mathematical logic to something as informal as a drinking game. Second, there is the social commentary about a certain type of person -- the one who brings up self-referential paradoxes at parties and thinks it is clever, while everyone else just wants to have a normal conversation and drink their drinks. The expressions of the other partygoers perfectly capture the universal experience of being trapped in a conversation with someone who thinks they are far more interesting than they are.
References
Bertrand Russell (1872-1970) was a British philosopher, logician, and mathematician, famous for Russell's Paradox, which concerns sets that contain themselves. The paradox in this comic is a variation of the liar's paradox and Russell's self-referential logical constructions. Russell's work on the foundations of mathematics, particularly in "Principia Mathematica" (co-authored with Alfred North Whitehead), explored exactly these kinds of self-referential logical problems.