The final scene of "cH - Fixer": Matt discovers his Primes are gone, drops his brand new Xbox, and gets kicked in the balls by Graham. The joke is the culmination of about 15 minutes of setup and almost every subplot in the series up to that point.
The "Mailbag" video indicates that this scene is Paul's favorite punchline in the history of the site.
In the season two episode "The Arms Race", Matt and James treating their Nerf war as Serious Business was mainly funny. Then Paul, misinterpreting a request from Graham, appears with a handmade weapon that is essentially a Nerf BFG, Up to Eleven.
Graham: What we're going to do is pat you down...(pats Alex down, revealing several hidden cards)...and we're going to watch you very closely, while you face...Kathleen.
Paul is a walkingCrowning Moment Of Awesome factory throughout this spin-off. He decides to start playing Magic: The Gathering, but he applies his general "professor" attitude to it in order to get the best results. In other words, he goes insane with research, testing, and searching, creating the best decks possible. Just watch the second episode to see how far he goes. And it works.
And, during a tournament, Paul places third place, despite it being his first tournament and first time playing against anyone other than other crew members.