Your profile says you are 18 or above, so that should no longer be a problem.
Well, get a job, then you can buy anything you want.
Really!? Unless you have a television crew following you, why wouldn't you try the frickin' store!
The mall, Wal-mart, duh...
OK, let's take this in simple steps:
1) If your profile age of 18-21 is correct, you are an adult. Start acting like one and being afraid of your parents finding out.
2) Large retailers like Walmart & Target do not report purchases to the buyer's parents.
3) Exactly what would happen if they did find out? Would they disown you? Murder you? Stop giving you boxers for Christmas?