It's a tossup between my bust and my feet.
I would say probably my bust wins out though, because with perseverance I *can* find shoes that work. My bust, by contrast, is something that troubles me each and every day, in terms of both fit and comfort. Literally every other part of my body, from my narrow face down to my size 6 feet, is very small. But my bust is just huge in comparison. Aside from the fit issues, it is uncomfortable and definitely affects my posture, which in turn affects my sense of confidence and polish. I don't know anyone else my size who has a bust as big as mine and it makes me feel like a freak.
Also, I have had the privilege of meeting many YLFers in person, and one thing I get told consistently is that I am much smaller in person than I appear in my pictures. I'm sure my chest size is the culprit in making me look larger than I am in my pictures. When I first started posting, I was told I looked like a forum member who was a size or two bigger, and while it didn't trouble me at all (she was very stylish and fab), it did perplex me.
As far as fit goes, anything fitted is a challenge. Most of my fitted clothes show some tension lines around the bust, and inevitably button gaping is frequently a problem. While I do embrace voluminous styles, I know they aren't as flattering on me as they would be if I had a smaller bust. It also interferes with my style persona and being able to wear the styles I like to their maximum potential. I were a B or C cup, I would probably be able to wear just about anything I wanted.
Ultimately I choose to just ignore it and dress how I want--within reason. I'd rather wear what I want and have it be a 7 or 8 than wear clothes and styles I don't like and be a 10. I try to do a little give and take: If I surrender my waist in a sack dress, I still keep the neckline fairly low (within my comfort level) and the hem nice and high. If I wear something fitted, I allow myself to wear a higher neckline and keep the hem lower.