I gave you Tinker vs. Des Moines first for the very reason that I hoped it would help you make the distinction between the two circumstances. I then listed two other cases that explain the situation in greater detail but you didn't bother quoting (as I can only assume because they didn't help your case).
But if you truly truly cannot see how showing your underwear is not the same as wearing armbands, expressing yourself non-disruptively, or making a statement then I honestly have no more to tell you. You seem to be under the assumption of many flawed ideas. I've quoted bills and court cases and you've given me argumentative ideals. I gave documents that show why school differentiates from the street, you have yet to even to even look at them.
I do hope you will look into the topic more, but I honestly cannot do anything more for you on my on. Perhaps read up on the subject: I had to read this for a law class before I switched majors. It is very cut and dry, but it is a treasure trove of information. This has a bit more of a relaxed feel; and while it doesn't go as in depth as the other one; it still explains a lot about the history and court cases revolving around free speech.