Derived from the Hispanic dessert served throughout the southwest, flan is sexual
slang for a near-vanilla person. As you can be straight without being narrow-minded, you can be flan but not
vanilla. The BDSM / fetish / leather world has often used
vanilla to define someone who is not into any kind of kink. Often it has a negative connotation, so flan is a positive word for the same thing. They may like conventional sex themselves, but they support your right to enjoy yourself in a safe, sane, consensual manner.