Although it seems most likely that the whole order never went into the system, i haven't had this problem before and i frequent this drive thru quite often. I would never rat the guy out because it is a horrible existence that these guys live working at this McDonalds with no real hope for a better job or better opportunity. They have to deal with drunk students on a nightly basis who constantly harass them and are out of control but i will take my business to Taco Bell and Burger King more often if this happens again.The McDonald's guy working the window was in business for himself with maybe a partner on the grill. The whole transaction never saw the ordering system/cash register and the employee pocketed your entire amount. Most likely he forgot you had a discount coming because that would only show up in a legitimately entered order into the store computer system on the printout-receipt.
Rat him out if you want - but me personally - would let the a guy make a few bucks when he can in a shit job like that..Old as the hills scam in restaurants and bars, even fast food joints..Especially at odd hours when there is little to no management around.
Most likely good inventory control at the store will identify that they have a thief and they will catch him sooner or later..
wil..