The ability to drink a beer extremely fast, but without anyone noticing you taking a sip of it. As in, you have half of a beer left but your friends is empty, your friend Schlundted the beer.
According to Donald Trump, Hillary Clinton got schlonged by Barack Obama in the 2008 democratic presidential primary. This is akin to getting screwed; slighted; severely whooped; underhandedly beaten; having your ass handed to you ,etc.
She (Hillary) was gonna beat (Obama), she was favored to win (the 2008 Democraticpresidential primary), and she got schlonged, she lost.