In later seasons of "The Big Bang Theory," the core group of friends embraces the later years of adulthood by starting families of their very own. They also begin new traditions by forging their own paths, like Leonard (Johnny Galecki) and Penny's (Kaley Cuoco) unforgettable festive outing. While it begins as a cheery day fueled by fitting Christmas music and outfits, it quickly dissolves into a nightmare that makes this flashback sequence funny every time you watch it.
In Season 10, Episode 12, "The Holiday Summation," the "Big Bang Theory" gang shares their less-than-ideal Yuletide celebrations. Sheldon (Jim Parsons) and Amy (Mayim Bialik) venture down to Texas to visit his mother, where they land themselves in an uncomfortable argument. Meanwhile, Howard (Simon Helberg) and Bernadette (Melissa Rauch) experience their first holiday as parents with heartwarming results. Last, but certainly not least, Leonard and Penny attempt to cut down their own Christmas tree, with a hysterical outcome.
The couple gets more than they bargained for when they realize the joyous activity is actually quite exhaustive and messy. The side-splitting sequence even reminds viewers of Galecki's time in the beloved film "National Lampoon's Christmas Vacation," where he showcases his specific sense of humor. It gets even funnier when they finally get the tree to their apartment — and find they've also brought home an uninvited visitor for the holidays.
Before Penny and Leonard can finally relax from their holiday excursion, they have to get the massive tree up the countless flights of stairs. This brings us another uproarious exchange, especially when Leonard eventually takes the break he insists he doesn't need. He succumbs to the exertion of force and lies underneath the festive pine tree for a brief moment of relief.
The unfortunate incident gets even funnier when Penny and Leonard think it's finally over. They sit together on the plush couch to catch their breath before they're made aware of the unwanted pest lingering inside the tree. However, rather than show a slapstick sequence of the couple getting rid of the rodent, there's a comedic quick cut that allows us to fill in the gap.
The cherry on top of this priceless scene is the way Leonard and Penny deal with the problem. They throw the tree down the apartment building's broken elevator shaft, tying the seasonal episode into one of the longest-running gags of the series. The result is a hilarious payoff to a silly mishap that becomes a timeless joke for long-running "Big Bang Theory" fans.