Flash mobs are a relatively new form of group expression that has received much online viral success. Hundreds of flash mob videos, each with millions of YouTube hits, can easily and quickly be found. Recently, savvy marketers have begun to use flash mobs to engage their consumers and to replicate the viral success of unbranded flash mobs. Yet as consumers become more familiar with ‘branded’ flash mobs, they become less easily engaged, and thus marketers see their persuasion attempts more frequently fail. In a time when some marketers are having true marketing viral success with branded flash mobs, this paper examines why many attempts to make flash mobs go viral fail. By conducting a number of focus groups where participants were asked to discuss their reaction to flash mob videos and their willingness to show them to friends, the researchers found that (i) consumers are unwilling to watch and share flash mob videos if they are not creative, if they do not arouse a positive emotion (e.g., excitement or amusement), and if the video does not show an audience that is affected by the performance; and (ii) consumers have an aversion toward corporations and are less likely to share a video when they realize that it is made for commercial reasons. As marketers increasingly invade public spaces with flash mobs, public policy issues are also considered. Copyright © 2013 John Wiley & Sons, Ltd.