A person with a personality that changes based on the other people they are with at that specific time. The "tofu" person has a generally bland personality when alone. They seem to temporarily absorb the thoughts, actions, and believes of those they are with.
Stephanie- "Jon is so tofu. He is a total jerk when he is around Will, but he's so sweet when it's just him and me."
'Tofu' as used to describe a person. Tofu is a bland and tasteless food item on its own. It is only when you add it to a dish full of meats and vegetables that it takes on the flavoring of all its around and becomes something.
Tony joined a gym and now he's all in the meathead scene. Total tofu