I am already in my pajamas

"... I am already in my pajamas" was originally supposed to be Professor Farnsworth's catchphrase, used to explain why he lacked motivation to do something.

However, the line was only used twice in the entire first and second run (in the first two episodes, "Space Pilot 3000" and "The Series Has Landed") after which it was abandoned.

The line has been picked up again for the third run, in "How The West Was 1010001".