I have no idea how it started, but even though Cars came out in 2006, Lightning McQueen's catchphrase "Ka-Chow" appears to have taken off as an ironic meme last month according to Google Trends (though the phrase with a hyphen reached a smaller peak in 2013 for some reason).
[direct use of the Google Trends embed code is no longer allowed]
A notable derivative is this "Croc-chow" image of a pair of Crocs, especially in this context in which someone was removed from a group chat.
This seems like it might have come from or been popularized by the me_irl subreddit, but I wouldn't know because I don't browse it.