Two things that are always hard to adjust to in Mexico--US.
1.) The Toilet Paper Issue.
When I get to the US, I am usually looking for the trash can... and then remembering that I can just flush it. In Mexico, it takes a couple days to "go back to the right way".
2.) Carpet or The Shoe Removal Issue.
I forget how almost all US houses have carpet. Therefore, mostly people pad around in socks or barefoot. I forget that walking around barefoot on my tile floors in dusty Fresnillo usually leaves me depressed at how quickly my feet turn black.