I too agree with Joe. To an extent. Anything not tznius all year (i.e. clothing designed and worn with the intent of clearly standing out — in a feminine way — to men) is not tznius on purim. Where I disagree is in practically every other way. Pretty much.
99 percent of “hilchos” tznius are dependent on minhag to some extent or another. Thus, would I have a teenage daughter who requests my input my first questions would be “what’s everyone else doing?”; “who do you anticipate interacting with in what way?”; and “what do you want to do?” then offering some advice.
If my wife were asking I’d probably defer to her (better) judgment.
If nearly anyone else were asking, I’d likely reprimand them on the lack of tact and tznius inherent in the question before declining to answer.
And obviously, I wouldn’t be the abhorrent hypocrite with detailed opinions on the neighborhood’s costumes.