Definition: The argument that since something is popular or everybody is doing it, so should you. Think of peer pressure or popularity as being the basis of the argument.
Example: The "Rachel" haircut that was wildly popular in the late nineties is a great example. Women who watched Friends all of sudden had to have the same exact haircut. Since Jennifer Aniston “debuted this style as the character Rachel on Friends in the '90s, more than 11 million woman have tried the cut. Fifteen years later it's still a frequent request, making the "Rachel" one of the most popular hairstyles of all time” (Kennedy, 2010, pg. 1).