I used to work at Dairy Queen. It was an okay job at the time. It got worse as it went along. I eventually got a better job, but I quit that too. Now I'm sporadically employed.

Anyway, I'm here today to give you the insider's tips on how to annoy the workers in Dairy Queen that hate you even before you go up to the window. Yes, I hated you too. But now that I don't work there any more, I feel free to tell you this stuff.

By the way, I've personally experienced all of these myself, and more...

Here we go!

Say "I want a Flurry"
This works on many different levels. DQ doesn't sell Flurries, they sell Blizzards. The worker can't be sure that a Blizzard is what you want though, so they have to ask. If the worker says "You mean a Blizzard?" you know she's already annoyed.

Note also that you didn't specify which size Blizzard you wanted. In fact, you didn't even mention what flavor!
Order other items they don't sell
Turtle sundaes are a good example. They are copyrighted by another company and the workers can't actually say 'Turtle'. Thus, they must ask you "Is that a sundae with Hot Fudge, Caramel and Pecans?" Make sure to say yes in such a manner that lets them know they are a complete idiot for not knowing such simple knowledge.
Mumble inchoherently when ordering
When you do this, they have to ask what you ordered again. Just for fun, mumble for a second time. Then when they try asking again, interrupt them before they complete their question and repeat your entire order LOUDLY and sloooowly as if the worker is a complete moron.
Change your order
Change or cancel parts of your order either right before you pay or right after. Most likely they've already started making the order and they'll be too meek to object.

HOT TIP: Change the flavor or size or cancel the drink orders first and blizzards second, since they're supposed to make them in that order (everything else, ie: cones, etc. comes after drinks and blizzards)
Pay everything with twenties or higher
The best technique is to flash your wallet in front of them and allow them to see all of your bills. This lets them know you have smaller bills than a twenty, you just aren't going to give them to the worker since you want to take his change.

HOT TIP: Pay with a fifty right after the store first opens. The workers never have more than two tens on hand at that time.(they never start with twenties)
Ask inane questions
If you spot a very small Dairy Queen like the one I worked at, walk right up to the counter, ignore the menu, and ask "Do you sell hamburgers here?" (or, better yet, read the menu, fail to find hamburgers, and then ask). Since they don't, get angry with the worker you are dealing with and order a hot dog or something, all the while making it clear that you don't approve of the fact that the owner has made decisions that are out of the control of the worker (ie: the owner decided NOT to make hamburgers a menu item). Make sure to take out your displeasure on the worker as much as possible.
Let your kids have free reign.
The workers are trapped inside their building and can do nothing about the screaming kids two feet away outside their window. So let 'em bang on the windows, throw things at the windows, stick their grimy, sticky hands into the service window, scream at the top of their lungs, and do whatever else their little hearts desire.

HOT TIP: Let your child pay for the order with the entire contents of their piggy bank. Not only will it take too long for them to count it, they'll always have enough for the product, but never the tax! This usually results in a double bonus since the other workers probably have already started the order in impatience and will have to change it since your child doesn't understand the concept of 'tax'.
Grab plastic spoons, napkins, etc. from the inside of the service window
The workers put out napkins for you and give you spoons themselves. If you want some pure hate to be elicited, grab them yourself by reaching inside their service window. For an added bonus, don't grab just one, but a handful.
Drive in and out of the parking lot.
If they aren't busy at the moment, drive into their parking lot, sit there for about five minutes, and then drive off. This will drive them crazy since they usually suspend whatever they were doing before you came in order to take your future order. They'll probably stand there as long as you sit there. Try it! It's fun!

Alternatively, if they are busy, just act as if their parking lot is a main road and zoom through it.
Say "Is this your first day?"
I've been asked this my first day, my sixth month, my first year, and on several other occasions. If you need a put-down dressed as a semi-honest question, this is it.
Stick your face into their sliding service window
This one is fun. Not only is sticking your face in a tiny, open service window annoying and illogical, the employees are required to keep the window closed unless money is coming in or food going out. Thus, sticking your face in that open window puts the employee in a quandary. If he closes it in your face, you can get all indignant and yell at the employee for shutting it in your face (one customer went so far as to actually punch the window). If he keeps it open, he gets in trouble with his anal-retentive boss and you are free to breathe germs all over their sanitized counter.
Order Odd Things and Return them.
Here's one I haven't personally experienced, but would be fun to try out. Go to DQ one day and order a Sundae...but with ketchup, or mustard, or the favorite condiment(s) of your choice. The employee will ask you if that's what you truly want, and insist over and over again that it is. When you finally get it, take one bite and then say "Bleech! This tastes horrible! I want my money back!"
Perhaps you should bring a videocamera for this one. It is surely going to be priceless.