To imbibe the majority or entirety of an alcoholic drink in an aggressive manner, sometimes as a result of peer pressure or due to third party coercion.
Jon: Shit, I've only got one Stella left
Alex: Neck it
Alex: What's your aversion to necking it you little herbert?
Chris: Neck it
A slang term meaning to hang oneself with a Noose-like object.
I'm just about ready to neck it.