the kind of feedback you don't want to give...

Take it from me... it is HARD giving someone feedback, and I've had to give quite a bit in my 7+ years in the business.
I'm not naming names, but everyone has something to learn from the bits below, and my mom tells me that giving feedback is character building....

•    Smoking right before you come into an interview.... don't do it.  I know that Interviews are stressful, and you may need a nic fix before you sit through an hour of torture, but please give your interviewer about a 10 minute grace period - and some major gum time before you enter the interview.
•    Same goes for smoking & coffee... nothing beats a Timmy's (or Starbucks) first thing in the morning... but please don't forget to brush or chew some serious gum before the interview.
•     SMILE! (nuff said)
•    Deodorant - wear it. Can't stress this enough.  If you are scent sensitive, there's an app for that.
•    Perfume / Cologne - please wear responsibly
• Eye Contact....... I can't say enough about this.... look at me when I'm speaking, and please don't look at the table when you are speaking.  It's not nice to stare, but several seconds of straight eye to eye combat is not creepy. 

I think that the reason these topics are generally more sensitive to approach than others like "you have something in your teeth"  or "your tie is crooked", because they have to do with that person's personal routine.  Just remember, that how you take feedback (Constructively vs. Personally), can impact your ability to get a job..... And if someone has worked up the courage to give you this feedback, it's usually to help you, not pick on you.