As far as Relative Strangers is concerned, let me save you some time:
Wealthy, well dressed, well groomed, cultured people are evil.
Poor, loudly dressed, unkept, obnoxious people are good.
However, concerning Idiocracy, I would have to say that I really enjoyed it.
Yes, there was a lot of very crude humor and a lot of cursing, and most of the characters remind me of South Park, Beavis & Butthead(not surprising, as this is a Mike Judge movie), and Jerry Springer.
The basic premise is that an average modern person(in 2005) is part of an experiment where he is to be placed in suspended animation for one year. Something, as usual, goes wrong, and he doesn't wake up for 500 years, a la Buck Rogers.
The main character has a number of trials and tribulations, but eventually is put in charge of fixing the world's problems because he is the smartest person in the world. All of the world's problems are due to the idiotic nature of the people living in the 2505 world. The crops don't grow because they are being sprayed with a sports drink, and the reason is because water was abolished as a beverage so that the sports drink, and in addition, the sports drink "has what plants crave. it has electrolytes." Not that anybody in the future knows what electrolytes *ARE*, which makes it even funnier when the "dumb" people are explaining to the main character in a completely serious way that the electrolytes are important.
I highly recommend, but I do warn about the crass humor. Try to look beyond the fart jokes.