In all my times of being to WDW, I have only met 1 really rude one. There was one that was not very nice, but she wasn't really RUDE, either. I encountered them both on the same day (our last day) of my Florida trip with my HS marching band.
The really rude one was working at Rosie's All-American Cafe in MGM (right across from the Fantasmic! theater). There were like 5 or 6 of us all going there for dinner before heading over to see Fantasmic! We ran into another friend of ours and her boyfriend and this friend was in a bad mood (nothing unusual for her), but we asked her what was wrong and she starts flipping out about one lady that worked there. She told us not to go to the second window (I don't remember which window it was exactly) because that lady was nasty. So we went up to order and the rude lady didn't have a line, while the other windows had lines with 5 or 6 people at least. Of course I went into her line because I didn't feel like waiting. As soon as I step up to the window, the lady goes "What do you want?" in this nasty tone. We had meal coupons that got you a "free" entree, drink, and desert at this restaurant. We had one or two every day of our trip, so by this point, we know the drill. I said "Could I please have chicken and...." She interupted me midsentence and said "Drink" in the same arrogant, nasty tone. I said "Diet Coke and..." once more, she interrupted me and said "What you want for desert?" and once again in that tone. I said "cookie please." When I went to hand her the meal coupon, she just ripped out of my hands. So then I went to the next window to pick up my food and after one of my friends ordered, she came over and I asked her if the lady was nasty to her too. My friend said "Yeah, she just took the meal coupon right out of my hands when I went to hand it to her." When we got to the table, everyone else said the same thing, so I know I wasn't just imagining it.
The other lady was in the parking lot the same day. We were walking to our buses to go home and we were following the asst. band director (really cool guy that acts our age at times, in fact all the staff does, you should have seen our band director get on the bus that night. Oh boy, was that interesting.). So the asst. band director starts walking in the middle of the street (not the brightest thing to do at park closing when all the Disney buses are coming in, I'll admit, but whatev.) Of course we follow him because we're slightly delusional at this point in the trip and have no idea where the buses are (I don't even think he had any clue, lucky guess is my story). The one CM was standing there flipping out at us for walking in the street. She def. could have said it nicer, but I guess its her job, so I won't say she was rude, just not cheery like the stereotypical CMs.
Ironically, that same trip we met probably the best CM I have ever encountered in all my trips. We still talk about him on a weekly basis more than 9 monthes later. I am so glad we met him because he kind of overshadowed the bad.