A lurking pun is the worst pun, one the offender has been waiting to spring on you.

The line is a comic complaint about premeditated wordplay. A “lurking pun” suggests not a spontaneous slip of wit but a joke held in reserve, with the speaker waiting for the right conversational opening to “spring” it on someone. The humor comes from treating puns as minor offenses and the punster as an “offender,” implying that the social cost of a pun increases when it feels engineered rather than incidental. It also captures a familiar dynamic: listeners often groan less at the pun itself than at the sense that the punster has been steering the exchange toward a payoff. The quote thus satirizes both pun-making and pun-enduring etiquette.