I'm not talking about eating tofu, but the expression that means something more like taking advantage of someone. What exactly does 吃豆腐 mean, and where does this expression come from?
I've only heard it used in describing sexual situations, and wiktionary.org describes its usage as follows:
A typical example would be some creepy guy pinching the flight attendant's backside as she walks past.
There's also a good discussion at wordreference.com.
I found an origin story on chinese-forums.com, but I'm not sure how reliable it is.
吃豆腐 refers to sexual harassment or men being frivolous with women.
Apparently it refers to a Tofu-shop a long time ago where the husbands rubs the tofu at night and the wife sells it during the day. To sell more tofu the wife flirts with her customers and the customers even grope her. The jealous wives of these "customers" will afterwards complain to their husbands: "So you went out to eat tofu again"
Edit: I can't find the real source of the story, but you can find it on many Chinese sites. It's probably a tale. About the translation, there are many possible gradations. I can go from "I (will) take advantage of you" to "I'll molest you" (actually it can both be in the past, the present or the future). Sometimes 吃豆腐 can also mean to crack a joke, but it's not the most common translation.