Christina Aguilera -- Birthday Diss to Mickey ... You Dirty Rat!

Christina Aguilera wanted a picture with Mickey Mouse when she went to Disneyland for her 34th birthday (not weird at all) -- but when the Mickster tried to go on break instead ... things got ugly.

Let's just say someone got called an a**hole -- and we know Mickey hasn't cussed in years. Not since that whole Minnie and Donald Duck thing, anyway.