Terry Vaughan is a former British Royal Marine commando, body language expert, self defense instructor and expert marksman who was a contestant on the precision shooting series Top Shot, which makes him exactly the man his daughters’ potential suitors do not want to greet at the front door.

Even worse — for them — is that Vaughan has literally written the book, Not with My Daughter, on how fathers can evaluate potential suitors in just a few minutes via body language and other clues.

And while Vaughan says the image of the aggressive rifle-polishing father is the “go-to default emotional setting” for many dads, it’s absolutely the wrong move if he wants to learn about the boy who wants to date his daughter.

“As a former British commando, I love aggression,” he laughs, “but you’re not learning anything. If you intimidate him, you’re overly aggressive, you’re sitting there polishing your knives, you shut him down and you’ve lost that chance to figure out who he really is.”

Instead, fathers — and mothers, too, Vaughan encourages — can learn a lot in a small period of time by putting the prospective suitor at ease, building rapport and “asking him questions that coach him into answering as relaxed as possible so you have a baseline of reactions. You’ll get more information from people being nice than you will just being aggressive and scaring the crap out of the poor guy when he gets there,” he notes.

Vaughan outlines several areas in which anyone can, with practice, learn to translate even small, subtle body language clues into telling information about a person, ranging from gait and posture to clothing, facial expressions, gestures and more.

“How much space somebody takes up is very indicative of attitude,” he says. “If somebody’s feet are wide they’re taking up more room than is necessary for comfort. Someone who takes up a great deal of space, lounges on things or has expansive arm or leg position, that tells you a lot about arrogance. And someone who’s arrogant doesn’t like hearing ‘no.’ If your daughter is smart, ‘no’ is something she’s going to be very well practiced in and understand that’s a complete sentence. She’ll know if she says it, it’s the end of the discussion, not time for a debate. [For] people who don’t like hearing ‘no,’ that’s the start of a negotiation.”

Chin position is another telling in-dicator.

“A chin that goes down protects the neck,” he says. “A chin that goes up is a little bit contemptuous because it exposes the throat. That tells you a little bit about attitude as well. If Junior does a head nod where his head goes up and he exposes his throat, he’s already told you he doesn’t feel threatened by you, which is completely and utterly abnormal if he’s at your house meeting Dad. He should feel very much threatened already.”

Now if a suitor shows up feet clamped together, taking up little space and, in fact, seems to be shrinking by the minute, Vaughan says parents shouldn’t take a victory lap but, in fact, try to put him at ease.

“You want to bring out the guy who’s in there,” he notes. “It’s great that he’s petrified — for the dad’s ego it’s great — but you’re still not learning anything. Warm him up and figure out who he is.”

In fact, Vaughan says the most important work in meeting potential boyfriends is the relationship between Dad and daughter — groundwork that can be laid years before boys start showing up at the door.

“If Dad and daughter have a great relationship and she can trust him to be on her side, and she can trust what he may be saying about her potential boyfriend is honest and supportive of her, that will ease the process of screening any guys,” he notes. “If dads are gonna get aggressive about the screening of the boyfriend but haven’t talked to the daughter about why he’s feeling a little tempermental then it’s going to backfire no matter what. And, in a lot of cases, dads are pushed to the periphery, only there as an aggressive bull in a china shop.”

Instead, Vaughan, who has two daughters — 13 and 10 — and a 9-year-old son, encourages moms and dads to be united in establishing an open, honest relationship with their children in which they talk about everything.

“We’ve had every conversation you can imagine, age-appropriate of course,” he says of his family. “We have a very open and honest relationship across the board. Even the tough subjects have already been discussed so nothing’s uncomfortable for anybody. If you can do that as a dad, go talk to your kids about everything, then so many other topics are much easier to broach. When it comes to dating, if your daughter is open to Dad as well as Mom, I think you’ve laid the foundation and groundwork where she’ll make the smartest decisions for herself and it’s much less likely that then Dad has to put his shotgun to use and scare off some reprobate.”

Vaughan says this groundwork laying should be done well in advance because children date, which will happen whether parents like it or not. “It’s gonna take Dad years to get his head around saying, ‘I’m gonna help you find love. I’m gonna help you use my years of experience to screen your boyfriend, not because I’m trying to stop you from dating, but because I want you to find the right guy,’” he laughs.

“When we had the sex talk, it was [my wife] and I, we sat down to have that conversation. We set a precedent that anything they’re going through, the questions they had, could be answered by either parent.

If Mom’s not here I can answer and vice versa. If you don’t run away from that as a Dad, if you’re available and you’ll openly discuss any of this, there’s nothing the two of you can’t talk about.”