In one episode, Fred visits this tuba player's apartment and offers to play the tuba himself. First, Fred took a deep breath into the mouthpiece and said "Nothing comes out." He was later instructed to blow thru buzzing lips. On his second try, Fred is able to make the tuba produce sound, but it emits a funny farting noise. What makes it funnier is that the camera closes up on Fred blowing into the tuba raising his eyebrows.
In some episode intros whenever Fred would zip up his sweater when he reached the part of the song that goes "Let's make the most of this beautiful day..." He would stretch the word "beauuuuuuuuuuuuuuuuutiful..." as he zipped his sweater. Sometimes Fred would even grin into the camera as he did so.
King Friday XIII and Lady Elaine Fairchilde are probably the funniest Neighborhood of Make Believe characters to watch as an adult. Several examples:
King Friday's adjustments to new fatherhood: in one episode, he attempts to teach Prince Tuesday (who is only two weeks old) subtraction, and at one point decrees that babies get too much attention and all babies in Make-Believe will be limited to one hour attention per day, before Cousin Mary and Handyman Negri deduce that the King is feeling overwhelmed with the demands that his new son makes, and he reconsiders when she offers to babysit.
Lady Elaine attempting to convince King Friday to let her spy on X The Owl when he wants privacy; dressed in camouflage, she suggests he may be building bombs and training secret agents. King Friday doesn't buy it.
When Lady Aberlin confronts Lady Elaine about her pressure on Ana Platypus, Prince Tuesday and Daniel Tiger before they start school, she responds with "I don't understand your pedagogy!"
Lady Elaine's birthday song for King Friday in episode 1450: You're older today, You're older today, You're older than you were yesterday. You're older than I am, Much older than I am, It's your birthday, You're older today!
Dr. Bill Platypus got King Friday good.
King Friday: *Reading from a Bill of Health* "After having examined Mayor Maggie and Neighbor Abercrombie at my tower office, declare that they are both entitled to clean Bills of Health." [...] "Of course, touching a wheelchair could never make anybody sick, anyway, and those who think so are unfortunately superstitious." Hmph!
In episode 1353, Prince Tuesday has a squirt bottle that he's playing around with...and he squirts Lady Aberlin in the face with it, causing her to shriek and scold him for it. Darkly humorous, but there is something really downright hilarious about a normally sweet and easy-going lady get driven to such frustration in the span of a fraction of a second (don't worry, she gets better fairly quick).
The entire last chapter of the book Dear Mister Rogers is this. After going through all the letters that ask simple questions based on childhood curiosity, the ones to help them deal with feelings, and all the heartwarming ones alongside the Tear Jerkers, the book closes with all sorts of humorous letters that you tend to expect — or not — from a child with a developing understanding of the world. One of them, for example, is from a kid who thought that the penny actually depicted Mister Rogers on the front and the trolley on the back. Another is about a kid who was dealing with upset feelings as usual, but when her mother said to beat up a pillow instead of kicking a cabinet door, her response? "Mom, you've been watching too much Mister Rogers!"