Mark Meechan, of Coatbridge in Lanarkshire, was found guilty of communicating a "grossly offensive" video in a Scottish court on Tuesday.
The 30-year-old vlogger taught his girlfriend's pet pug to react to the phrase, which he repeated 23 times in a video seen by the court.
Meecham, a self-described "professional s*** poster" and free speech advocate, said the video had been taken out of context.
The video was watched more than 3 million times on the video sharing platform. Meechan was arrested after sharing the footage in April 2016.
He told Airdrie Sheriff Court that he made the video to annoy his girlfriend Suzanne Kelly, 29, and denied any wrongdoing.
Speaking after the verdict, he said: "There has been a huge miscarriage of justice.
"I think it is a very, very dark day in terms of freedom of speech and freedom of expression.
"One of the primary things that must be considered in cases like this is context and intent and today context and intent were completely disregarded.
"For the system to disregard such things means that your actions no longer matter - they decide what your context and intent is.
"For any comedians making jokes in Britain, I'd be very, very worried about your future because - the context and intent - apparently they don't matter anymore."
Comedian Ricky Gervais rallied to Meecham's defence, writing on Twitter: "A man has been convicted in a UK court of making a joke that was deemed 'grossly offensive'.
"If you don't believe in a person's right to say things that you might find 'grossly offensive', then you don't believe in Freedom of Speech."
Meecham is due to be sentenced on April 23.
