B.R.
First of all, a 6 month old shouldn't be in a backpack. A front carrier is much better, and he won't pull hair. I hate front carriers, too, because they (as well as backpacks) put all of the baby's weight onto their lower spine- I prefer slings and wrap carriers, but that's just me. Also, you can say no and squeeze all you want but it's probably not going to make a difference. A 6 month old doesn't have quite the grasp of cause and affect to understand this. However, if you continue to do it he will eventually grasp it. In the mean time, put your hair in a pony tail- hair pulling is just something babies do!