I'm really not someone who gives or seeks advice all that often, and almost all of what I have given has been OK and received has been excellent.
Worst advice I ever gave: this is easy. A few years ago a friend asked me who he should draft as his fantasy league quarterback-Peyton Manning or Ryan Leaf (both were rookies). I told him to take Leaf, because he was going to be a star, while Manning was going to be average at best.
Worst advice ever received: As a former King of unrequited love (I will pause here so that you may dry your tears............) more than a few people suggested I not express my feelings to the object(s) of my affection. Well intended, I'm sure, but I wasted a hell of a lot of time waiting for someone in the dark to see the light, while all the bulbs were burned out.
Wow, that was a really horrible metaphor. My supreme apologies.