Im surprised no one has mentioned the hygiene aspect of PJ wearing in public.
Its like a statement of 'i havent washed today, in fact, I havent even changed out of the garments I slept and sweated in while I was sleeping last night'.
I see people in goth, punk, leathers etc... and I know at least, they bothered getting changed out of what they slept in (unless they are particularly rumpled I suppose!), and I know they are using their clothes to make a statement about the music/lifestyle they are into.
I see someone in PJs in public and the lifestyle statement screams 'dirty smelly lazy skanger'.