My best advice-stay away from it. Unlike weed,the high doesn't last.. when you do coke you just want more and more of it. I was into it for a while when I was around 20...spent a lot of money on it and had a hard time quitting. It makes you do shit to get more that you would never do to get weed--beg, steal, borrow, make friends with the lowest of the low.
All that being said, trying it once with a buddy won't ruin your life---unless you end up liking it so much that you "try" it again, and again....