It's a long story, I hitchhiked across the border from Paraguay to Bolivia with a smuggler in the middle of nowhere and since there was no official border crossing I had a predated Paraguayan exit stamp which the Bolivian immigration at the Brazilian-Bolivian border didn't accept, so they banned me from Bolivia. The immigration in Brazil was more helpful and had the idea to ban me from entering Brazil for "entering the country without a passport" so they could give me an exit stamp with which I could then enter Bolivia. Not sure if I'm still banned from Brazil actually :D