Now, although Mc Donalds is famous for it's advertising, and making the whole world think that the Bic Mac is the best thing to come along since sliced bread, each restaurant is as amateur as a new-found business. Not only is all the employees rather inexperienced at what they're "supposed" to do, but they will just loose all control when an emergency occurs. Here we go:

First, gather a few friends (4 is good) and enter the Mc Donalds resturant, talking loudly reaking of some strange smell, that automatically makes that old couple sitting by the door leave. If one of those pimply-faces goons is wiping the floor, then track some crap all over it (you could pretend to slip and break your head, but you might actually do so). Next before you get the food, find a table. Start yelling and releasing some strange body odor, so anybody would leave their table and walk out the door. Sit 2 friends there, and go up to the counter with another. Find a place where the line is short, or if the line is long say "I only wanna buy a coke", and most people will let you move up. Now you get to the ordering (heh heh heh).
Somebody "always" must want a plain hamburger with absolutely nothing on it, this takes extra time to make, and drives the little hamburger-makers insane. Then order a 9-pack of chicken McNuggets..No a 20 pack..No three 6 packs..wait..go back to the table and ask your friends and ask who wants what, while your other friend stay by the counter and makes a pass at the clerk. Get back to the thing and order three 6 packs of chicken, etc.
Now she asks: "What kind of sauce would you like?". Of course, say that you all want barbecue sauce, one of your friends wants 2 (Only if there are only 2 containers of barbecue sauce left, then they have to go into the storeroom to get another box. Finally the drinks, somebody wants a coke, somebody a root beer, and somebody a diet coke. After these are delivered, bring them back and say: "I didn't order a diet coke! I ordered a sprite!" This gets them mad; better yet, turn down something terrible that nobody wants to drink, so they have to throw the drink away, they can't sell it.

After all the food is handed to you, you must NEVER have enough money to pay. The clerk will be so angry and confused that she'll let you get away with it; another influence one her is to get your friend tell her: "If you let us go, I'll go out with you" and give her a fake phone number. Now, back at your table. Somebody likes ketchup and mustard (too much), and someone likes to use a lot of napkins. Another likes forks and knives, and just keep breaking those plastic ones. Have all your friends yell out: "Yay, we have munchies!!!" as loud as they can, that'll worry the entire restaurant.
Proceed to sit down, so you're sitting in the smoking section, then while none of the tobacco-breathers aren't looking, grab a sign from the other side of the room which says: "No smoking" so he have to move. He then goes into the "real" smoking zone, and gets yelled at. He then thinks that no smoking is allowed in the restaurant, and goes outside to eat, maybe even in the rain. After your meal, and a lot of ketchup packets smeared all over the the table, try to leave, but oops, somebody has to do his duty at the men's room. As he goes there, he sticks an un-eated hamburger inside the toilet, and flushes it a while, until it runs all over the bathroom. Oops..Send a pimply-faced teenager to clean it up. (He won't know that that brown thing is a hamburger, and he'll get sick, whee!!)
As you leave the place, looking back at your uncleaned table, somebody must remember that they left their chocolate shake there, the one's that's most full. He takes in, then yells: "This taste like crap!", then he take the lid of, and throw it at the garbage can, but oops..he missed..Now the same poor soul who's cleaning the bathroom now has to clean up to chocolate shake. Leave the place, reversing the "We're open" sign.

Congrats, you have just put all of Mc Donalds into complete mayhem, and since there is no penalty for littering in a restaurant, bugging people in a public eatery, you get off scot-free.

Wasn't that fun?