If people are doing things in a passive-aggressive kind of way (or even an "I'm a lazy wench and don't want to work" way) it's often best to draw attention to the inequities right off the bat. For instance, you're getting your assignment in report, and you realize that you have Mr. Circlingthedrain who has lots of needy family members and will probably die about 45 minutes before your shift ends. On top of that, you've got Ms. Brittlediabetic with the glucose drip and Mrs. Dementedunsteadyonfeetandunrestrained. I think it's reasonable to inquire whether the assignment might be reconsidered based on the fact that the rest of the patients include Mr. Walkietalkie, Miss BeingDischarged, Mr. IshouldbehomebutI'vegotreallygoodinsurance and Mrs. StoicIdon'tneedanythingandallmyfamilylivesblessedl youtofstate.
Once you're knee-deep in the assignment it becomes more difficult to switch, but if you're working there regularly and regularly getting the shaft, you need to bring this up in a non-confrontational way, and if they still screw you, then hit the road. Eventually they'll figure out they're only screwing themselves. Or not. Either way, not your problem
Good luck - let us know how it goes!