Eating tofu doesn't mean any part of a girl's body. This sentence should be liked by people in some areas. The exact meaning of this sentence is to take advantage of others. For example, when you are walking with a girl you know, you suddenly give her a hand. Or more ambiguous contact. Give her a kiss. The other person can also say that you eat her tofu. There is no limit to which position, as long as she thinks you have taken advantage of her, she can use this sentence to describe it. People in some societies used to like to say that.