Pajama bottoms - or perhaps you refer to them as "loungewear" - are not to be worn in public. I shouldn't see you wearing them in Starbucks, the grocery store, the laundromat, or walking your dog. And I REALLY shouldn't see you wearing them on an airplane - especially while you are carrying a pillow. This is not a sleepover, its a flight. With other people. It's not nappy-nappy time. (I know this bothers my buddy at the [cherry] ride as well.)
Wearing pajama bottoms in public tells the public several things about you:
1) You're disrespectful. Clearly you don't give a shit. If you had any respect for yourself and/or others, you would properly dress before going outside your home. Even a Walk of Shame ranks higher on the ego scale than you.
2) You're irresponsible. If you have to wear pajama bottoms because everything else you have is dirty or at the dry cleaners, then you must have a time management problem. There are classes and lectures you can take to help alleviate that.
3) You're immature. The only time I've worn pajamas in public was . . . ok, I have never done it. Children can get away with it, but somewhere around the age of, oh I dunno, 4, it's just no longer acceptable.
4) You're lazy. If you don't care enough about what you look like, what kind of shape must your home be in? Your bathroom must be disgusting.
5) You're dirty. Chances are if you haven't bothered to change your clothes, then you also haven't bothered to shower or bathe. You may as well just wear a sign that says "My body parts stink so don't get too close".
Now if a fire broke out in your apartment and all of your clothes burned up, or maybe your ex cut them all up after an argument, or you were robbed and the only thing they took was your clothing, maybe possibly THEN it would be socially acceptable to see you walking around in pajamas. But even that is stretching it.