I've had two that have had a lasting impression:
An old friend (friend no longer), and the NC State admissions guy.
I was two years out of college when I decided to apply to vet school. I knew it would be an uphill battle because I had extra courses to complete, a miserable GPA to fix, and NO experience at that point. Everyone was supportive of me except one "friend" who insisted on multiple occasions that I was making a huge mistake. His old girlfriend had strived to be a vet her whole life, and it took her 3 application cycles to even get admitted, so how did I think I had a chance, making the decision so late in my life? He insisted it would therefore take me a minimum of 3 applications to even have a shot. I wanted SO BAD to get in on my first application, almost not so much to get in but to prove him wrong!! Unfortunately, my first application was woefully unprepared, and I knew it, but I just wanted to get my name out there and get started while I was getting experience. BUT luckily I did get in to TWO schools on my second round, and I haven't spoken to my old "friend" since 2005....
The admissions staff at NC State (my in-state school) used to meet with every applicant individually and go through applications in detail to help you get in the next year (which I still think was a really good idea and they should have continued doing it...) The one admin guy I met with was nice enough throughout the entire process, pointing out some of my strengths and weaknesses, until we got to the grades/GPA section. He flat out told me that with a 3.2 I would NEVER ever get into vet school, and that I needed to pursue another undergraduate degree to get my GPA up in order to have a fighting shot, and that I should definitely not bother applying the following year. I suppose, now, I understand he was probably talking about me getting into NCSU, because I just didn't have the GPA to make their cuts, but he pretty much crushed my spirit for a few good weeks. Luckily I didn't listen to him (about not applying -- I did follow the rest of his advice), and I somehow managed to be admitted to two out-of-state schools. It may be more expensive, but at least I'll end up at the same place =)
Don't let ANYBODY tell you you can't! I'm so lucky to have the worlds most supportive parents, boyfriend and friends, who would stick by my side no matter what I choose to do with my career.