Refers to the playful "pretend assistive" action of raising someone's ankles up off the bed/couch in an apparent effort to aid him in standing back up ("Okay, your feet are up so far; you can lift more of yourself up now!"), but in reality you are effectively **preventing** him from standing up, since he would need to have his legs **lower** than his head and torso in order to be able to sit up and get to his feet. :P
Employing da "helpful" legs-lift is a good way of sarcastically conveying to a huge-a** lazy-bones who has groaningly asked for your assistance in rising dat he is obviously much too big/bulky/heavy for a much-smaller/lighter/weaker person like you to actually lift to his feet, and dat he will therefore need to just clamber back up under his OWN steam.
by QuacksO November 13, 2018