Interestingly, this insult is more often delivered with words rather than with the actual candy. In the right context, gifting the candy is not an insult at all. For example, someone who is preparing for an exam often receives yeot as a gift, as an encouragement to "stick" the exam (=pass the exam.) But of course, there is no mistaking the intent behind the toffee shower that the the national team received.
Several of you also emailed to ask how the Korean felt about the way in which the players were received. His feeling is: they probably don't deserve it, but it is part of the job description. Certain players--Son Heung-min comes to mind--played their hearts out, and definitely did not deserve to be told to "fuck off." Ideally, one should be able to focus-fire the insult. If one threw the yeot only to those who deserved the most blame, striker Park Chu-young and goalie Jung Sung-ryong would be getting a cannonball of candies to their faces.