jgnat is spot on, this is a game of endurance, and you will win! Just fly under the radar for now.
Do you have a plan for the next 4 years? At 18, I am assuming that you are probably in your senior year of high school (if you are in the U.S.), or graduated a few months ago? Are you getting some further education? What are you interested in? Not everyone wants/needs to do 4 years of college, but if you do to pursue your dreams, how will you finance it? Do you have a part time job right now? Look at all of your options, make a plan. Talk to a college/ h.s. counselor. Maybe all you need is a 2 year degree, or a certificate program. Have short & long term goals. If your parents are against further education, use whatever reasoning you know will work to sway them. If a 4 year degree is what you desire, you may have to start out at a junior college, as that is affordable, local, and probably less scary to your parents. You can then transfer. Take the time to figure out what YOU want!
You're young, you have your whole life ahead of you, and it's going to be a wonderful journey with some bumps along the way that will make you stronger and wiser.
And did you let your Mom know about the creepy older man's comment and that it made your skin crawl? How does he know what the young men at your hall think abour your attire? Are they complaining to him, or is he taking a survey? That, my dear, is your "stumbling block"!