PDA was first mentioned in The Strange Case of Origami Yoda. Hannah and her giant boyfriend did it during Fun Night. 

PDA was revisted in The Surprise Attack of Jabba the Puppett when Kellen saw Rhondella kissing John Oxley prior to the spelling bee and became so upset that he may ahve lost the spelling bee because of it, mispelling recommend r-e-c-c-o-m-e-n-d. Whether that was the reason or not, Rhondella lost by mispelling 'youthful' (y-o-u-t-h-f-u-l-l) after he had gone up and he was forced to sit next to her in an agonizing awkward silence. John Oxley came in scond place "and Rhondella was like, 'Woo-hoo!'" -Kellen