Neck up means to ask someone to stop speaking un-truths. And it also is a non polite way to persuade a person or individuals to cease their conversation, or to "shut up".
Hodgo: "Union players are all gay champ, bogans are fairdinkum tops"
Jango Fett: "Neck up cocksmoke/belter!"
To tell a person to commit suicide by means of hanging.
"Why don't you do yourself a favour and neck up you cunt? Your a Parrot! Fucking blowfly.." Keithy Goerge to Chopper
The act of forcing ones premature departure from a non relevant discussion, whilst holding your thumb perpendicular to your neck and index finger directly toward the sky.
In the words of Chopper "Neck up, parrot"
inserting head up anus till neck is up the anal cavity
neck up you fuckhead
The definitive way to tell some one to "Shut their mouth"
"Neck up"........... CUNT.
"Neck up",,,,,did i ask for your fucking opinion.
"Neck up",,,,FUCKHEAD.
If in Australia, and someone is hanging around and you can't get a word in,you can say "Neck up you Blowfly',cunt likes the sound of his own voice.
The fine art of getting totally red necked out, by the way way of demeaner, manners and overall disregard for general social acts.
Terry-"The Coca Cola 600 is this weekend and we've got tickets"
Chuck-"Time to get necked up boy!!"