I’ve never even heard of lucid dreams before, but I remember often in my dream not wearing any pants or underwear. What does this mean?
It means that you are in fact a nudist and should not wear any pants in real life unless on your head.
Nah, I’m kidding. Not wearing any pants is a common thing in dreams. Although I’m not that good a the interpreting-common-dreams-symbols game, I’d say it’s just your mind working on embarassing situations and representing them in your dreams.
Yeah (partial) nudity is a common dream theme. I don’t think there’s a single explanation of it; you have find the explanation within yourself. But very often it’s a sign that you should open yourself to new possibilities, or that you need to work with embarassing situations (as davidr mentioned). It could also mean you are or will be putting yourself in a vulnerable situation, or it may have a sexual meaning, etc…
Damnit, why the hell am I the only one who hasn’t had this naked dream!? Everyone else has had it and im getting jeolous… 
Try this site, it’s handy dandy;
dreammoods.com/
(dreams open to interpretation, actual dreams may vary, get off my lawn)