Stan refuses to vote in the school mascot election because his choices are a giant douche and a turd sandwich. Unfortunately, his views on voting are seen as un-American, and he is ultimately banished from the town. 

The plot in which the students have to vote between choosing douche and a turd as their new school mascot, and Stan's apathy to voting in that particular election is an allusion to the 2004 Presidential Election between George W. Bush and John Kerry. It satirizes the apathy of many voters who felt that both candidates were equally bad choices for the President for different reasons.