Dude, I'll tell you what you have to do. I'm glad you asked. In order to unlock Ronald McDonald in Super Smash Bros. Brawl, first hit up your local 'Murican drive-thru and order up a McDouble.
Next, head home and fire up the game. Initiate a fight, and clash until you're about halfway to victory.
Then stop. Don't even touch your controller.
Cut the power, and wait ten seconds. Now, slot your McDonald's burger patty into your Wii CD slit. Afterward, a sub-menu will appear when you start the system up again. It will ask you if you'd like to challenge the optional opponent to a duel. Navigate to 'yes'. The screen might start to fizzle a bit here, since the hamburger meat has been reported to rub your system's interior components the wrong way.
The brawler will, you guessed it, pop out dressed in yellow overalls and a red wig. Here's the trick: you have to feed a dollar into the disc slot in order to win. Otherwise he does this one-hit kill move that you can never dodge or block. And you must be fully clothed. No shirt, no shoes, no service.
After you've met the necessary qualifications to complete the battle, Ronald will hand you a form to fill out to review your fighting experience. As long as you give him good marks, he'll appear in your character roster. Whoever you were fighting him as gets replaced by Ronald, so use some two-bit nobody likes, such as Chun-Li, Cesar Romero, or even Colonel Custer.
I even hand-picked some good let's plays of how to do this perfectly.
Tips on proper 'Murican ordering etiquette (
http://www.youtube.com/watch?v=Q16KpquGsIc)
A look back on 50 years of putting the 'Happy' in 'Happy Meal' (
http://www.youtube.com/watch?v=wCF3ywukQYA)
Lara Croft and Sam admit their lesbian love for each other with a passionate kiss (
http://www.youtube.com/watch?v=H5npPPkSMF4)
How the West was Won (
http://www.youtube.com/watch?v=2KE0nl54EkQ)
Hope this helps.