Actually, I can tell you exactly how hard it is. I practice in both dress clothes and casual clothes outside of class.True enough. My purpose in using a do-gi is solely as a practical training garment. It is durable, cheap when you consider how many times you wash and wear one, and it soaks up sweat readily if you use a heavy enough weight of cloth.
If you want to simulate wearing street clothes, you should have a street clothes training session with shoes and all. No gis, no sweats. I imagine some of us will be shocked to find out how difficult high kicks are to pull off when you are wearing a slippery pair of wing tip shoes with a coat and tie.
My daily clothing is actually pretty conducive to taekwondo, with my shoes being the most non-helpful part. Pivots are much harder with actual traction. I have learned to do all of my kicks pretty well in street clothes, but it has taken practice.
I do agree: a street clothes training session is a great idea. Or wear a dobok or gi all the time and deal with the odd looks.
Daniel