McDonald's

I come to this place a lot and always have great customer service and great products. After the past 3 days worth of failed attempts to get a shamrock shake in Augusta, I decided to come here.

They have the shake but they also wont allow for half shamrock and half of another flavor (i want chocolate). I don't see how it is more than acceptable for a customer to customize their burger with whatever extra they want or what they don't want, and how a customer can order french fries no salt....but yet a customer can't order a shake half of one flavor and half of another.

And once again, I worked for McDonalds for 3 years so I know that this process is very easily accomplished, so why can't I get my half and half shake?