To put my comments in context, I believe what my mother told me many years ago: that dressing nicely is an easy way to be polite to the people around you.
What you're wearing here tells me that you're really not interested in doing that: your shirt isn't tucked in and your shoes aren't tied. You might be going for a particular look of some sort, but these things tell me that you're really not interested in the being-polite aspect of dressing well. Instead, it tells me that you couldn't be bothered to spend the time to do things like tucking in your shirt and tying your shoes, which reflects on how much you're trying to be polite to others.
But then I'm probably not the sort of person who'll be at this party. It certainly could be the case that their opinions are completely different. You're probably a better judge of what's appropriate for them than I am.