but Cuba is an auto-transcribed closed caption which appears when the "Leo Laporte Blows up at Mike Arrington on the Gillmor Gang" video is played with "Transcribe Audio" turned on. The "but Cuba" caption appears when Leo says, "Fuck you guys!"
The phrase was discovered during the NSFW episode titled "But Cuba". The phrase was such a hit that there was no question that it would be the title of the episode.
Leo had heard the phrase, but did not know the origin. He was fully briefed about the origin of "but Cuba" during The Trials of King Leo and has since begun using the phrase himself.
But Cuba, the original episode of NSFW in which it appeared.
Tom Merritt slipped a "but Cuba" into his final episode of Buzz Out Loud.
The Trials of King Leo, in which the origin of the phrase is explained to Leo Laporte.
Numerous other NSFW episodes after the "But Cuba" episode.
Leo LaPorte (google transcribed): Screw you of soft money all off, but cuba. I'm not kidding of done.