Starting at the "end" of the back of the neck, join new yarn, and with a short circular needle pick up stitches around the steek. Be sure to pick up the first/last stitch of the steek. If you did not set aside a stitch at the bottom of the neck, increase one stitch at the bottom point of the neck.
When you've completed picking up stitches and have knit (plain) across the back of the neck, begin knitting in Knit 1 Purl One Ribbing, being sure to mirror left-to-right at the bottom of the knit (i.e. if the last stitch before your "point" or "bottom of the neck stitch" is a knit, then you should knit the stitch right after the point.) Always knit the "point" stitch. Additionally, on this first row you should do a centered double decrease at the point.
My favorite centered double decrease is a "slip 2 together, knit 1, lift the two slipped stitches over the knit stitch."
Continue knitting the collar, in this ribbing, doing one double decrease every other row, for an inch and a half. Bind off normally.