... As he, another colleague that I know quite well (and would describe as a friend) and I all went to leave through a small section between two counters, he put his hand on my back (kind of as though pushing me with what felt like a finger or a few fingers, and with pressure).
... In attempt to communicate my confusion at being touched to him, I stopped walking and gave him a sort of confused and unhappy look, but all he said was "you first", as in, he was touching me on the back to allow me to step through the counter first. ... I should probably also mention that I wasn't stood in front of him, I was stood sort of to his left, which made it even stranger to me that he would touch me there.
You are with someone else and he steps in to apply force to you from behind, when you question his actions (with a look) he tries to either turn it around or deescalate the situation and calmly say "you first".
You were first already, and going, but he's entitled to push into your space and physically push you. He's essentially say 'get going, darn well hurry up' - saying "excuse me" is the more polite way to interrupt you and your colleague, waiting a few moments is even a wiser move. The new guy either doesn't know his place or you're someone, some woman, in his way.
He attempts to turn around his pushing by simply trying to make it seem like he had important advice to offer; "you're in front of me, get going".
It's ignorant or rude.
Understand that it is likely just his way (others have described it as a cultural thing) and not an attempted assault, but that neither means it's desirable nor acceptable. Part of the problem is that it is "his way" - like you actually needed him to be present and to physically guide you through life. You might view it as domineering or demeaning. If he wouldn't do it to a really large man that he didn't know you can be certain that he knows it's an unwanted action, but that can be difficult to determine.
Next time you might want to "communicate your confusion" then and there by insisting that he go first, if he questions your actions politely explain that "You want to ensure that he doesn't reach out and apply his all knowledgable guiding hand, that you can work this out without physical contact". That allows him and out if it was simply a momentary lapse of judgment and a spotlight if he thinks he is correct.
Don't go overboard on a single error in judgment (maybe you were dawdling and everyone behind him was pushing him, 'tell those two to get going ...') but at the same time don't accept being thrown under the bus, him (move aside woman, man coming through).
Why you are correct to object to this behaviour:
In an article on Workjax titled: "The Four Zones of Interpersonal Space" it is described this way (I'll quote the minimum):
"One of his chapters (in Dr. Tony Alessandra's book "Charisma: Seven Keys to Developing the Magnetism that Leads to Success") is dedicated to the use of space and time. He describes the four zones of interpersonal space and how to use them effectively.
- The intimate zone is within touching distance, from actually touching to about two feet. This is the space reserved for people who genuinely care about each other. Lovers hold hands and parents carry their children or put their arms around them protectively. It’s rare to see this space penetrated in business settings. But when it managed effectively, it can send a powerful message. Women use this space more than men; they tend to reach out and touch people more often.
[It seems like he was able to go out of his way to slide-in a situation where he feels he can justify his actions - explain politely and clearly that it's not necessary, that comes across better than explaining that he's not to do that.]
The personal zone is from two to four feet. It’s used for discussions that are private and not meant to be overheard. In a busy networking meeting or at a party, people will avoid breaking this barrier if you are engaged with someone else at this distance. If you’ve ever been trapped by a bore and waited in vain to be rescued, try moving another foot away. It will open up your space for someone to enter.
The social zone is four to twelve feet apart. This is the space used for public and casual social conversations. It allows others to enter into the group. It can be fascinating to watch people conversing in a group; they resemble fish in a school as they move in and out to make a comfortable space for new entries.
The public zone is more than twelve feet. Public speakers and important figures use space to distance themselves from their audience (and establish authority, since demanding more space is a power signal.)".
That is how one doctor describes the situation.
A similar explanation is offered on Wikipedia's webpage on proxemics in the section on cultural factors and interpersonal distance:
"Edward Hall, an American anthropologist and cross-cultural researcher, described the interpersonal distances of man (the relative distances between people) in four distinct zones: (1) intimate space, (2) personal space, (3) social space, and (4) public space.
Intimate distance for embracing, touching or whispering
Close phase – less than 1 to 2 cm
Far phase – 6 to 18 inches (15 to 46 cm)
Personal distance for interactions among good friends or family
Close phase – 1.5 to 2.5 feet (46 to 76 cm)
Far phase – 2.5 to 4 feet (76 to 122 cm)
Social distance for interactions among acquaintances
Close phase – 4 to 7 feet (1.2 to 2.1 m)
Far phase – 7 to 12 feet (2.1 to 3.7 m)
Public distance used for public speaking
Close phase – 12 to 25 feet (3.7 to 7.6 m)
Far phase – 25 feet (7.6 m) or more.
The distance surrounding a person forms a space. The space within intimate distance and personal distance is called personal space. The space within social distance and out of personal distance is called social space. And the space within public distance is called public space.
Personal space is the region surrounding a person which they regard as psychologically theirs. Most people value their personal space and feel discomfort, anger, or anxiety when their personal space is encroached. Permitting a person to enter personal space and entering somebody else's personal space are indicators of perception of those people's relationship. An intimate zone is reserved for close friends, lovers, children and close family members. Another zone is used for conversations with friends, to chat with associates, and in group discussions. A further zone is reserved for strangers, newly formed groups, and new acquaintances. A fourth zone is used for speeches, lectures, and theater; essentially, public distance is that range reserved for larger audiences.
Entering somebody's personal space is normally an indication of familiarity and sometimes intimacy. However, in modern society, especially in crowded urban communities, it can be difficult to maintain personal space, for example when in a crowded train, elevator or street. Many people find such physical proximity to be psychologically disturbing and uncomfortable,5 though it is accepted as a fact of modern life. In an impersonal, crowded situation, eye contact tends to be avoided. Even in a crowded place, preserving personal space is important ...".
I appreciate that this was a lineup situation and that there's a "small section between counters" but it is incorrect for the "new person" to try to be the alpha dog (Definition sources: #1, #2).
I wouldn't try to overblow the situation if you are able to simply and easily convey that you don't want him to reach out like that. Maybe he likes you, a lot.
He needs to understand that he has in fact thought it OK, apparently even positioned himself, to leap over a few boundaries in a single bound. It's literally pushy, demeaning and even belligerent between males.
Don't feel you are wrong to tell him his actions are wrong.