"Biology 101": Leonard mocks Jeff for eating by himself in the cafeteria. Jeff tells him to shut up and says he heard about his prescription socks. Leonard raspberries back.
"Documentary Filmmaking: Redux": After Jeff indicates he's always willing to go the extra mile to avoid work, Leonard interrupts saying "Like sex with women". Jeff tells Leonard to shut up and that he smells like mentholyptus. Leonard then indicates he's thinking of breaking into the TV game. He doesn't want to look back and wonder "what if".
"Foosball and Nocturnal Vigilantism": After Shirley agrees to help Jeff beat The Germans at foosball, an eaves dropping Leonard says "The stakes have never been higher". Shirley replies "Shut up Leonard! I found your Youttube page. What's the point in of reviewing frozen pizza? Leonard replies, "You're talking about it." Shirley replies, "That's true."
"Regional Holiday Music": In the end tag, Leonard does raspberries to "Carol of the Bells".
"Urban Matrimony and the Sandwich Arts": After Leonard corrects Jeff that they are at the rehearsal for Shirley's wedding and not the actual wedding, Jeff tells him to shut up and that the teenage girls who are playing ping pong with him are doing it ironically. Leonard is also seen hugging Annie and crying when Shirley and Andre make up.
"Contemporary Impressionists": Uncharacteristically, Leonard tells Jeff he's looking good. Jeff replies, "Thanks Leonard. For that compliment and for your service to this country".
"Digital Exploration of Interior Design": Leonard takes couch cushions for Abed's pillow fort. Jeff complains that he was going to lie there. Leonard says "I was going to invest in IBM in 1952, but life is full of disappointments." He was also in Group Study Room F when the war between Pillowtown and Blanketsburg begins.
"Pillows and Blankets": Leonard was a member of Pillowtown and it is mentioned that he fought in the Korean War for North Korea and his nickname was "Bucket of Guts". He participates in the final battle in the cafeteria.
"Virtual Systems Analysis": It's revealed that Leonard was hiding in the bushes when Jeff and Annie kiss in "Pascal's Triangle Revisited". As to why, he says "I don't have cable" and shrugs.
"Basic Lupine Urology": Leonard is seen arm wrestling in Pierce's gambling game. When Troy and Abed arrive he yells, "Youth! Scatter!".
"Course Listing Unavailable": Leonard loots from Subway's topping bar in the Greendale riot. He says he's going to take everything except onions and olives.
"Curriculum Unavailable": Leonard is part of the Study Group in the insane asylum clip.
"The First Chang Dynasty": Chang's second in command Joshua shakes Leonard's can of pop which then explodes on Leonard when he opens it.
"Introduction to Finality": In response to Britta telling Jeff that she'll be practising her pysch skills on Abed and what's the worst that could happen, an eaves-dropping Leonard says "Classic tee-up". Britta replies, "Shut up Leonard! I know all about your crooked wang!". Leonard says, "No such thing as bad press!". He also appears as the baliff in Dean Pelton's "courtroom" and reviews "Let's Potato Chips" in the end tag.