30 Rock Season 5 Episode 5 (30 Rock s05e05) with title “Reaganing” aired on Thursday, October 21st 2010 at 08:30 pm via NBC Network.
Here is summary for 30 Rock Season 5 Episode 5 :

On show night, Liz Lemon grows increasingly infuriated when no one seems to remember that it’s her 40th birthday. Just before the taping, Tracy Jordan becomes convinced that nothing is funnier than a performer laughing and breaking character, which he elects to do all night