I REEEEAAAAALLLLLLLYY hate that too! I either get toilet roll to to put in my hand when i open the door to leave or i try to open with my elbow or foot which is very hard to do i might add!
I work with alot of people who have Degrees, Phd's etc etc.... but its amazing how many dont know how to flush a toilet or use a toilet brush!
On a similar note, I equally hate it when they wash their hands but don't dry them, so the door handle is then soaked. Sure it MIGHT be clean water, but it just feels so wrong! I then try do the same as you and open the door with my foot as I hate touching the wet door handle, it proper gives me the shivers.