By the way: I once tried to explain the German expression Ich geh' mal für kleine Jungs/Mädchen
to a South American guy, but obviously I failed, since he replied You can come to jail when you do that in my country
Man...talk about some dangers when speaking a language that is not your first.
Ok, as for the United States. Well, at least for my state, Pennsylvania, since it can vary in each region.
It is unusual for friends (boy to girl, girl to girl) to kiss each other, and boy to boy friends handshaking while under 18-21, but over 18-21, it becomes more common. Hugging between friends is more common than kissing...boys and girls often do this together.
When you meet the person, a handshake is usually required regardless of age.
Kissing is also often restricted to relatives. Boys should kiss and hug their aunts, mother, girl cousins, and grandmothers, and handshake their uncles, boy cousins, and grandfathers. Girls should kiss and hug their grandparents, boy and girl cousins, father and mother, aunts and uncles.
You can see couple kissing on cheek quite often in public, it's unusual to see kissing with tongues, but it is not considered rude.
Holding hands is common and accepted.
Touching is rude, unless you want to tap the shoulder or arm to get the attention to let you know you dropped something, or for asking a question.
Keep your shoes on when coming in the house of a guest.
No burping or farting
Elbows off the table and use folks and knifes (unless you're eating sandwiches, breads, pizzas, and so on.)
It is rude not to hold the door for someone behind you. If you missed it, just simply try to catch the door and apologize, it at least shows respect and that you tried.
Call strangers Madam/Miss/Sir/Mister. I usually say "madam" for middled-aged and older ladies and "miss" for young ladies. And "mister" to men regardless of age.
Drinking in public (outside bars, restaurants) is discouraged and not acceptable.
If the table is long and rectangle, the most senior member of the family (like a grandparent) or the host sit the front.
If you accidently bump someone, it is rude not to say "excuse me"
It is rude to talk loudly on cellphone inside public places.
It is rude for letting your kid scream loudly in restaurants.
Well, that's all I can think of.