I have this theory -- one that probably doesn't hold an ounce of water -- about why so many members of my generation and younger feel comfortable wearing pajama bottoms -- including those thinly disguised as yoga gear -- pretty much anywhere short of work, weddings and funerals (though I'm sure it's been done.)
(Of course I'm talking about my own (anti?) fashion habits and I'm hoping you can relate. For the record, I'm pretty sure that I wore yoga pants for the first 18 months of my child's life. Maybe 36. *cough* Working from home is my enabler, pinky swear.)
Anyway. My theory about why we are comfortable wearing bedroom wear in public is this: I believe it can all be traced back to Madonna's underwear-as-outerwear Jedi mindtrick, otherwise known in my old Catholic school circle as the 'omfg, is Mary Margaret wearing a lace bustier as a shirt and are those rosaries around her neck?' trend. Catholic school was a bitch. I think we are so fully jaded about bras as shirts, boxers as shorts and the whatnot that any potential pajama bottom inhibition was stunted before it even had a chance to grow.
Also this: pajama bottoms are comfortable. I'd wear them all the time if it wasn't for the social expectation that I might wear something other than my pajamas to public gatherings. Heck, I wish they looked like my jeans so folks would stop hassling me.
PAJAMAS AS JEANS. An idea so good, someone beat me to it. PajamaJeans, 'Pajamas you live in. Jeans you sleep in.' [warning: autoplay audio so turn sound down or off]
PajamaJeans: also solving the common fashion dilemma that happens when you just can't decide - do I want to sleep or do I want to go to the rodeo?
I can't say I wouldn't at least try them on. 'Nuff said.