It’s every man’s nightmare: a girl (worse, a girlfriend) listening in on the type of candor he reserves for the boys.

It’s a rare life experience that I think only a handful of people have ever seen — sort of like the view from Everest’s summit or the inside of a UFO.

I can now say that I’m one of those few, ever since my maybe-boyfriend (you know the type) failed to properly hang up his iPhone after a standard post-workday chat. It was almost too serendipitous, like maybe it was meant to happen.

After talk to you laters were exchanged, I brought my phone away from my ear only to hear him suddenly speak. Thinking he had forgotten some anecdote of monumental importance, I stayed on the line. “Did you say something?”

He hadn’t, but what I heard next (my name) would ensure I stayed on the line for the next 12 minutes. Now, I’m not a natural snooper (definitely not so now — we’ll get to that) but I challenge you to resist listening in on the person you’re dating say the things he won’t say to you to a carload of his friends.

Even better, I knew every single person in that car — and could identify them by voice. (Don’t think I don’t remember what was said, Matt.)

It was much like the movies depict it. Nothing completely earth-shattering was said, but it was phrased in much bolder terms than would ever have been presented to my face. There was talk of which friends of mine were hottest (you know, in case it didn’t work out. I’m pretty sure you can just work a trade, right?), hypothetical ultimatums made with an unfamiliar bravado, and a lot of posturing affirmations of the perks of bachelorhood.

Once conversation finally turned from the juicy stuff to the impending basketball game, I hung up. Then I promptly texted a few choice excerpts and waited for the anxiety to kick in. I ignored a few phone calls for good measure, and then answered as casually as I could. I faked mad, but a few minutes into the conversation I could no longer suppress my laughter at the ridiculousness of the situation.

The fact that it had even happened was too much, and he was so truly traumatized (due to a far more spotty memory of what exactly he had said) that I wound up comforting him.

I knew somehow that it wasn’t really any of my business. I couldn’t be mad over thoughts that weren’t meant to be shared and hadn’t been acted upon. And I have a new vehemence in my condemnation of relationship tactics like going through text messages, reading e-mails or hacking Facebook accounts.

Not because you should trust each other, though that’s valid, but because I think it’s a genuinely bad idea to be privy to each other’s every thought or the dirty details of past relationships.

I was recently debating the value in serious, marriage-ready relationships of a sort of “come to Jesus” conversation before you make the big commitment. Whether it was advised that you sit down and reveal every possible indiscretion, every romantic (or casual) encounter, and start off married life with a clean slate.

I, for one, am against it. I don’t think the already pitiful divorce rate could survive that kind of transparency. People are jealous and overly sensitive, they assign meaning differently and they hold grudges. Better, I think, to draw a line in the proverbial sand and declare the past the past, and the future all that really matters.

When you’re in a relationship, especially a serious one, what space do you have if not the sanctuary of your own head?

As long as you remember to hit the “end call” button, that is.