I am mildly horrified I never knew this. According to Urban Dictionary—my go-to source for everything—“tofu” is slang for sex. I mean, I use everything as slang for sex, especially all things related to food. Here is what UD has to say:
A slang word for sex, popular in the Northwestern US and theCaliforniacoast. Mostly in Asian communities.
Derived from the expression “Selling Tofu”, a Chinese euphemism for prostitution
EX: Leah and Benjamin are in the bedroom having tofu.
How did I not know this?! Man, I need to start hanging out in Asian communities more often.