Stuart was feeling "chirpy" as he watched two squirrels in a walnut tree from his bed. Because Susie's mind was typically in the gutter, she assumed this to be a euphemism for the contents of Stuart's underwear. If only she had double carpeted her bottom step!
The phrase was stated in an interview with Whitney Houston when Diane Sawyer read a headline concerning the cost of Houston's drug habit. Houston, apparently assuming there were receipts from drug dealers and also apparently assuming Sawyer had them requested to see said receipts. The clip went viral in the form an animated .gif.