M.R.
This is a learned condition. I have three children (oldest is 8). My oldest pulled my hair, head-butt, and bit! The two younger children never did this, because I learned with the first ;) At this age (17 mos.) your child knows what "no" is -- it's not necessarily the word - but the tone. Try this (it worked for me) -- Voice a firm "NO" and sit the child down (out of your arms). He will cry, and climb back on you (probably). Take him in your arms again, but the next time he pulls - "NO", sit him down. Know that your children need your approval and they learn very quickly (providing you are consistent). Hang in there -- it will work ;)