I think it has always been common BETWEEN teenagers and other teenagers, and often persists into the early 20s. I suspect some of it is biological... establishing pecking order and dominance.
However, the epidemic of disrespect to parents and teachers and etc is more recent. It was very rare when I was in school (70s, 80s) but appears to be a lot more common now.
"Yes sir, no ma'am" seems to be rapidly disappearing from the vocabulary of anyone much under 35, unless they are prior military. Even my own son, who is widely praised for his good manners, tends to omit those honorifics because no one else his age does it either.
But sir/ma'am isn't such a big deal... the smart-ass-mouth on some young folks IS a big deal. I don't hear it directed at me much (I don't look like someone you want to provoke), but I do hear some ASTONISHING stuff directed at other adults by young folks and even children to their own parents.
There was this 19yo gal who wanted to travel to Europe with her idiot friends. Her father didn't think she and her friends were mature enough to go to Europe unsupervised, and declined to fund her trip. Now here is the kicker... she threatened to go to the local Platinum Plus and STRIP to raise the money! Daddy caved in... I would've kicked her ass out the door just for TALKING like that, let alone doing it... and all the crap I'd bought her (car, clothes, furniture) would NOT be going with her. "You wanna do it YOUR way, fine... but do the whole enchilada baby, and find a new place to sleep too."
Unreal. Spoiled brat.
I think it is a lot of things. Kids are too spoiled these days; too much TV and Xbox and not enough chores, too much given to them without enough work required of them. Not enough parenting, not enough saying "NO", not enough parents insisting on being respected as they should be. Lack of discipline in the schools. Zero-tolerance for violence in schools, leading to kids saying horrific stuff to their peers with no fear of getting their teeth knocked out as was the case when I was 18. General coarsening of society... media, like The Simpsons, South Park, and so many other shows with smart-ass foul-mouthed kids. Entitlement mentality. A lack of appreciation for what one has; too much "Me" thinking and not enough "We" thinking, but at the same time too much dependency and not enough self-reliance.
Then again, every generation since Julius Ceasar has thought the next generation was decadent, lazy, disrespectful and would surely be the downfall of the Republic. :