Public shitting
Here in Montreal, you already get ads while shitting in a public washroom. The company in question is called ZOOMedia. They pay to put ads in the can in bars and so on.
They are also a favourite target of culture jammers... up here, that's what we call the people who deface public advertising. Some of them are quite imaginative. For example, for a long time one could get instructions in how to open up the can ads (they're in a little glass fronted case) without the key from various websites. Apparently it took something like fifteen seconds to open one of those things up once you knew how to do it.
