EDIT FROM A COUPLE YEARS IN JAPAN'S PERSPECTIVE: Man I made a lot of mistakes back then.
Okay, so there is this word, meshiagarimasu, that is a polite way to say eat or drink. However, if you use a dictionary, it won't be there unless you cogitate it into its dictionary form (meshiageru). But the Japanese don't use/say the word meshiageru, only meshiagarimasu!* It's insane. Things like this make me laugh like a lunatic.
*:I checked this out with my supervisor and she said that maybe the emperor uses the suru form of the word. I guess important people are allowed to use rude versions of polite words ;)
If a commoner wants to use plain language they must use taberu (eat) and nomeru (drink).