I kind of had the same reaction. It's almost like there was some level of allegory that I didn't get. But either way I thought it was pretty funny. Not great, and certainly not classic south park, but funny nonetheless. Cartman + Anything minority related = funny. That song he sang was pure gold.
God damn it. Without fail, every single half-season the finale sneaks up on me. I never find out it was the last episode of the season until after I watch it. That said I found it funny, in part because I saw 2012 on Sunday. Cartman bringing up the Mayans was hilarious. I guess he thinks the Mayans were white. Also every time Kyle said somewhere that you just don't pee, and the other kids would just look at each other, I cracked up.
I really thought it was mehhh. The running joke with all the other kids admitting they peed in pool was the best followed by the monkey jokes. Cartman's story had potential but I didn't think it was that great. More Randy could have helped this episode.
I agree that they should have done more with the Cartman/minorities thing. In addition to Kyle saying something like "you just don't do that" in every situation where he learns someone pees, I thought the Italian owner talking about pee in his thick accent was hilarious. Also, they had already done the peeing in pools gag in the episode "Summer Sucks."
I think they should've done SOMETHING with the Cartman and minorities line. He sang a song, said he's a doctor and done. Nothing funny in that episode. Other than pissing on a monkey of course.