ok I'll make you a deal.... I'll post this but I want to see at least one collar by the end of the day!
1) find a raglan pattern you like and are familiar with. Starting with the back piece, sew to an arm along diagonal seam, then the front then an arm. Do not sew the last seam (arm to back) yet.
2) cut a wide strip of stretchy stuff... I like cotton lycra the best! Cut it wider and longer than you would normally (I like 1 1/2" strips) and make sure you cut it with the stretch going along the length. (you will trim extra length and width later)
3) sew the collar strip to the shirt neckline right sides together (i.e sew it to the front of the shirt), stretching it a little as you go (about the same as you would for FOE) -- I serge mine but a 1/4" seam would work too.
4)serge up last seam including collar. This makes it look a little like a turtleneck with a raw edge!
5) flip strip over and using a narrow double needle, topstitch it down. I don't pin, I just stop every few inches and making sure it is snugly wrapped around the seam.
6)flip over and trim strip neatly -- I find this gives a neater and easier finish than trying to catch a narrow strip evenly all the way around
7) voila!
8)lay the shirt on the ironing board, arrange the collar into the shape you want and hold the iron slightly above the fabric and STEAM THE HECK out of it to get rid of the rollercoaster! (if it doesn't get rid of it all, stretch the collar a tad more next time). Press firmly once it has been steamed to make it look pretty.