Worst advice I have ever recieved was "come on try it just once" Tried it and got hooked. It is coke and I am happy to say that when I realized that I had to have it I quit but not before I was spending $300 a week on it. Not much by some standards but it was way to much. I am proud to say I quit cold and have never gone back. It has been over 20 years now.
Worst advice I ever gave: Move to Atlanta. Now my best friend lives elsewhere. It was good for her just bad for me. =(