1.) Slang for blowjob, or oral sex performed by females.
2.) A way of someone receiving pain for stupid thoughts or ideas by giving them a hard slap on the back of their neck.
3.) The area between your head and your shoulders.
1.) Man, that ho gave me neck the other day!
2.) We should what?!?! Boy! That's neck!
3.) He has a giraffe neck!
to make out, among other activities, with another person. A rather archaic term for it (used particularly well in The Catcher in the Rye, for instance), sometimes used in the present day.
Although this implies suicide via hanging this is not a requirement.
"Hey , did you hear that Applebee's is no longer going to sell Long IslandIced Teas?"
"Yeah, I'm going to neck myself. Guess we'll have to drink somewhere else"