In Season 2 Episode 23 of Spongebob Squarepants, originally aired on November 16th, 2000, the character Patrick mistakenly asserts "No, this is Patrick" when asked "Is this the Krusty Krab?" after being hired at the Krusty Krab restaurant (shown below)
On November 4th, 2006, a thread was submitted to 4chan's /b/ (random) board asking "Is this /b/?" to which another user replied with a screen captured image of Patrick from the Spongebob Squarepants episodes saying "No, this is Patrick" (shown below).
On May 19th, 2007, YouTuber ItamiBukoto uploaded a mashup video featuring the Spongebob Squarepants scene combined with the "This is Sparta!" scene from the 2007 film 300 (shown below, left). In the first seven years, the video gained over 3.67 million views and 8,500 comments. On March 9th, 2008, YouTuber Born Reddi uploaded a similar 300 mashup video, gathering more than 790,000 views and 740 comments in the next six years (shown below, right).