There are perfectly legitimate reasons for still living with one's parents into adulthood. Someone I know is living in his in-laws' basement right now, because he was recently fired. Other people I know take care of parents with serious health problems. The issue with these people is not that they live in their parents' basements. It's that they're willfully ignorant. You can do that just fine living on your own.
I feel slightly singled out by this reply. I have to admit. I was certainly not deriding anyone for living with their parents into adulthood, if that is indeed what you were inferring about me. I would like you to explain how and where I have even suggested that I have no compassion/understanding for those that live with parents for care reasons or personal reasons, if that is indeed what you were inferring. If it was a more general response to the phrase, then I'll sit with that and feel less singled out. However:
The word
living invokes a slight subtlety into that figure of speech, namely individuals that
live fairly solitary lives and spend inordinate amounts of time
living in a basement in front of the internet.
I'm guessing that your friend does not
live in their parents basement, but rather sleeps there and during the day is trying to gain a job and rebuild their life.
In fact I am acutely aware of the impact that caring for parents has on people, especially teenagers. I've worked with many teenagers and young adults that suffer with depression because they are parent carers, and will probably remain with their parents well into their 20s and 30s.