Updog is a wordplay in a rather annoying but widespread joke. It only makes sense in the context of that jest that relies on the other half not understanding the expression.
– Bro, did you shower? You smell like updog.
– What’s updog?
– Nothing man, what’s up with you?
No one knows, who made up the joke, but probably plenty of people would take retribution for all the times they have been played by this simple word.
One of the earliest instances of it being seen on the internet was on Ars Technica Forums.
Since its first appearance, it has experienced a grand upheaval, appearing on Urban Dictionary as early as 2003. Updog has since been featured in season 2 of the Office in 2006.
In 2013, a series of updog jokes have been posted on Reddit, featuring scenes and characters form Game of Thrones, who were trolled without mercy.
Since then the joke had made it to BuzzFeed, YouTube as well as several other sites, where heralds of humor are exploiting the ignorance of others. The joke’s popularity is wavy, but it is constantly embraced by people who want to play a trick on others.