What’s the origin of the sexual slangs “necking”, “goosing” and “heavy petting”?
Re: Goose/goosing
Lighter, in his Historical Dictionary of American Slang, Vol. I says it goes back to English rhyming slang goose-and-duck. He gives an earliest cite of 1879. But the use at that time meant f***.
The earliest cite he specifically gives for poking someone in the rear with a hand is around 1938. But it certainly had to come from the earlier usage.
necking
The basic conotation should be pretty obvious.
Mathews, in A Dictionary of Americanisms cites it as early as 1923.
The basic conotation of heavy petting should be equally as obvious. Well, at least “petting” should.
Mathew cites “petting” to 1928. He also gives a 1924 cite which uses “petting parties”. Although, the term was followed with the word “snuggling.”
But snuggling probably leads to petting, which leads to…dancing? 
You asking 25 questions today smartt? Why don’t you get a dictionary & look them up??? onelook.com has plenty you can see for free.
"“necking”, “goosing” and “heavy petting”? are sexual? I don’t think so.
“Gooseing” also derives from the fact that geese, due to their average stature are prone to pecking at the genital region. Geese, being such agressive birds, have obtained quite a reputation for doing this.
Dude, I don’t remember the moment when I actually FORCED you to read my threads. But hey, my memory is not as good as it was when I was younger.
Didn’t Groucho once say “Whoever called it ‘necking’ had a terrible sense of anatomy,” or something similar?