Yeah you should be presentable when doing something like that, I mean if there was a lady who was well dressed and a lady who was in pj's. I'd take the makeup advice better off the well dressed lady, it just looks better as in it reflects she's more serious about the topic at hand :)
Im not a girl but image is everything when it comes to fashion..i suggestthat ifyou do the video that you only where a nice top and be close to the camera.there going to be focused on your face and upper body.make sure you speak well too just because its gonna br a ghetto YouTube video doesn't mean you don't have to talk well
So if you look really bad then the video has to be positioned where it's above your neck and aimed at your face more so than a whole body shot. You should be presentable, if not then it's possible no one is going to want to follow your instructions. I'm not a girl but I wouldn't mind PJs... maybe the hair... yeah I draw the line _____ on the hair
It does help make the makeup look complete. If you skip out on your clothes and hair, all that hard work you did with your makeup would look 'blah.' It's like painting. If you only painted the main subject (person, building, etc) and you leave out the background and scenery, the painting would be incomplete.
If you're doing this as a favor, I wouldn't worry too much about it. If you are wanting to do this professionally, I would consider treating it like a job and do everything the 'right' way. You could always cheat by wearing a nice shirt and leave your pajama bottoms on.