A passive aggressive way of asking someone to do something. Generally used to describe a situation where speaker's position is not superior to his or her audience, but you can tell they think it should be.
Derived from the annoying statement: "We Are Going To Need."
An alternate use evolved when it was shortened to 'wag': "He's always trying to wag me, but he's not my boss. He just tries to get everyone else to do his work so he can stay on Facebook all day."