The Big Bang Theory Season 1 Episode 9 : The Cooper-Hofstadter Polarization

Cleaning up after an internet experiment, Leonard discovers a letter in the trash can. He and Sheldon had been invited to present some research they had done together at an academic conference. However, Sheldon disapproves of presenting research in person and says Leonard cannot go without him. Leonard defies him and says he will go and present the findings on his own. This causes a rift between the two which Penny tries to mend but accidentally makes worse. At the conference Sheldon appears, tries to discredit Leonard's presentation, tries to "blow up" Leonard's head with his mind à la the movie Scanners and has a physical altercation with Leonard. In the end, the fight is captured by Howard and put on YouTube.