I'm familiar with the textbook usage of tambi?n in the context of "also" or "me too". I also hear it used in ways that make no sense to me. Here's two recent examples:
Me: "Come by the house to pick up the 100 pesos I owe you."
Motoconcho: "Tambi?n."
Me: {Walking my dog}
Passerby: "Perro tambi?n?"
What the hell does that mean? The context of the one when I was walking my dog was that he wanted to know if the dog was friendly.
Me: "Come by the house to pick up the 100 pesos I owe you."
Motoconcho: "Tambi?n."
Me: {Walking my dog}
Passerby: "Perro tambi?n?"
What the hell does that mean? The context of the one when I was walking my dog was that he wanted to know if the dog was friendly.