to swing neck

To swing neck means to suck, a gargantuan dick. So big, you can't do it by simply putting it in your mouth. You have to go to the point to deep throat the colossus and swing your whole neck (and upper body) back and forth to really suck the whole giant

Hey did you hear about how Melissa blew Michael?
Yeah! I heard she really had to swing neck to fit it in...

Hey, have you seen Johnny lately?
Yeah, heard he's been swinging neck by the corner!
Oh daamn! I knew he was gay but not that much!!