Do it as a parody and go all the way.
Since your skin is darker, shorts would be out if going the surfer or skater route unless you do the knee high socks thing. I forget where to get it but an online search should come up with the professional makeup to give you that "Chappelle show" white guy tone. Just be wary, the makeup is very thick, will rub off on clothes and will make your skin break out if worn for an extended period of time. What I would do, just as I did years ago when a friend and I went as "Milli Vanilli" on Halloween when they first got busted, make the clothes over the top and wear a big wig. If you get the combo right, everyone will get it regardless of the skin color. I used a mop head dyed black with a giant paisley bandanna, baggy jeans and tight t-shirt and "everyone got it"! Nobody even mentioned it being offensive, just hilarious.
For a generic "dude", get the surfer dude wig at any costume shop along with some over the top sunglasses. Some sandals with socks, not too baggy of pants and either a polo shirt or a longsleeve surf shirt. Dont forget to say "hey dude, my names Chad bro".
Now,
I would go 80's with it and be the black Crockett from Miami Vice with the surfer wig, sunglasses, loafers with no socks, gaudy color 80's sport jacket with the sleeves pushed up and white baggy pants. Dont forget to top it off with an over the top color t-shirt with the neck collar torn off. If you can, pick up one of those dime store plastic gold watches to go with it.
Some pictures for an idea
http://luna.nash-bridges-online.de/mv.html