The concept of "girl inches" is funny, especially to those of us with big dicks. It's hilarious to whip out 8 inches of cock and hear her say it must be 10 or 11 or even 12 inches. So what's the deal with girl inches? Are we men being lied to, or are women just terrible at estimating sizes? It's a bit of both, and some other factors too.
There are four primary drivers of the girl inches phenomenon: guys exaggerating their size to women, women exaggerating the sizes they've had, porn, and the general human tendency to suck at estimating the size of things we don't often measure.
Men lying about their size
Guys, this all starts with us. There's a lot of pressure for guys to feel like they need to measure up, and in the case of dick size quite literally. All it takes is one guy to say they're 7 or 8 inches long and then everybody is else is claiming that because they don't want to seem like they're small in comparison. And with the popular notion that "bigger is better" drilled into so many heads, the last thing you want to be is "small".
And when every guy is adding 2 inches, then that's the new perceived "average". So, gents, if everybody around you is claiming 7 inches or more, while that's technically possible, it's extremely unlikely. More likely is that they're lying about their size out of insecurity. If they all say something closer to 5 or 6 inches, then you've got a honest set of guys on your hands.
So, feeling like they have to keep up the exaggeration, the lies spill over into interactions with women. They're told that the dick in front of them is 7 inches when it's realy 5, and that matches up with all the other dicks they've been told were 7 inches. Short of busting out a ruler, they're not going to verify it. So the ladies trust what us guys have told them, or they've read the science and know what the average cock size is but believe they're some sort of unicorn that only attracts and thoroughly enjoys these larger (but actually average) penises.
So step one to fixing girl inches? Men need to be honest about their size with each other and with their partners.
Women lying about their experience and preferences
Women are already working with a skewed view thanks to the lies of men making them believe that 7 inches is average when that's actually a rather large and rare size. Add onto that the same "bigger is better" pressure that's driven into men leading to women believing that they too must prefer larger penises. So all the sudden there's childish one upmanship between the girls, with successive claims about the sizes of dicks they've fucked and how much they loved them.
Then you have guys hearing those same conversations about monster 9 or 12 inch cocks and all of the sudden they're feeling even more inadequate, and are further driven to exaggerate their size in order to woo these very same women into their beds. Any time you hear somebody say that they prefer and have had multiple 10-inch or larger dicks in their body, it's a guarantee that they're lying.
Most women are not like this, especially those that have experienced a truly large dick and understand the struggles that come with having sex with a guy that has one. But those are conversations generally had in private, while the ones that loudly and publicly proclaim themselves to be "size queens" are more likely full of it.
There is of course the joke about how women suck at parking, because men keep telling them that this [the joker holds up their hands about 5 inches apart] is 8 inches! [insert laughter]
Porn lies about everything
Don't get me wrong, there's absolutely nothing wrong with the idea of pornography. As long as everybody involved is a consenting adult, then it's totally fine. You can consume whatever variety of it you like. The problem is that porn is twice as bad as men in general at exaggerating the size of dicks. There are a number of tricks that the porn industry uses to make dicks seem bigger, to include small actors (both male and female), deceptive hand positioning, wide angle lenses up close that make things seem bigger, over-the-top acting, fake rulers, and questionable supplements and dick-damaging pumping.
But the biggest thing that porn does is just outright lie about dick size. Most porn actors are at least above average size, and some are truly large, but it's not uncommon to see them adding 3-5 inches to their measurements. If porn tells you that the 7-inch dick you're seeing is 10 inches, then when you're presented with a penis in real life your perception of size is going to be terribly skewed. It certainly doesn't help that you've got guys like Jonah Falcon lying about his size making it seem like the sizes claimed in porn are possible.
Remember: Porn is fictional entertainment. Take everything in it with a huge grain of salt.
Humans just suck at measurement estimation
We humans are not good at estimating the size of things, especially of things we don't regularly measure. Ask somebody how long their car is and they're bound to be off by a few to several feet. Point to a building and ask how wide it is. Ask how wide their wrists are.
Unless these things are something they're used to measuring, they're not something that people are likely to estimate well. We work off of known sizes and compare what we're seeing to our fallible memory. So it's easy to estimate somebody's height within an inch or two, because you know your height, you've talked to other people about their height, and can easily gauge what they've got. But then you get two guys who claim to be 6 feet tall standing next to each other and they're clearly of different heights, because some men can't help but lie about everything in their lives.
So that applies to penises as well. Granted, a lot of guys are used to dick measuring, but only their dicks. They only see it from above and around 18-24 inches away. In that one instance we can make a decent estimation because that's where our experience is. But when you see another dick in the locker room, you're bound to make a wrong estimation of its size, likely on the high side. Women are even worse off in dick measuring experience, since they usually have little-to-no experience measuring penises (in part because men don't want their lies to be exposed).
Lies, lies, lies
In the end, "girl inches" are almost entirely a byproduct of men and their lies. If we set realistic expectations from the start, then women won't have skewed recollections, and we won't feel like we need to keep lying in order to get laid (never mind that penis size is rarely a primary factor for women in choosing who they'll sleep with).
But it's a vicious self-perpetuating cycle to break. The lies pump up expectations which mean that the lies have to continue, lest you seem like you're not going to be enough.
As with almost all things in life, honesty really is the best policy for all of us.