These two issues can only be dealt with if we have a proper theology of our freedom in Christ. Both flirting and flaunting can be justified by a good legalist. People justify themselves by saying things like, “I'm not committing any sin and we're just having a good time” as well as “Well they shouldn't be looking anyway.” The problem with this reasoning is that it is ultimately selfish.

Dressing modestly. First, lets clarify some things. We are all personally responsible for our own sins. If I lust for a girl after seeing her cleavage, I am fully responsible. I cannot blame her nor justify my sin by revealing another's sin. That logic did not work when Adam blamed Eve for making him eat the fruit, and it has not worked since. (Genesis 3:12. The man said, The woman whom you gave to be with me, she gave me fruit of the tree, and I ate.) Likewise, my pension for lusting, does not justify someone else's disregard for my purity.
In 1 Corinthians 8, Paul addresses one way in which we should view our freedom in Christ. “Therefore, if food makes my brother stumble, I will never eat meat, lest I make my brother stumble.” He is talking specifically about eating meat but the principle applies to every aspect of our lives. The spiritual well being of others should always trump our own desires even if those desires are not inherently sinful.