shoulder tap
n.— «They wanted a six pack and offered him money to get it for them. It’s a technique known as a shoulder tap: An underage individual waits outside a liquor store and asks someone who is of age if they will buy them some alcohol. “You can keep the change,” one of the teens said as she handed the man a $20. “Hey, nobody’s going to know. It’s just beer.”» —“Teens film commercial highlighting shoulder taps” by Kevin Ryden Daily Mail (OIney, Illinois) Mar. 13, 2007. (source: Double-Tongued Dictionary)