If someone is propositioning you, it means that they are offering you sex. It is a more polite and euphemistic way of saying someone wants to bang you.
In the case where the prepositional phrase “in bed” is added to the end of a fortune cookie saying, the entire phrase will always makes sense and could potentially make you more appealing to your date.
In an attempt to captivate and entice Jill, Matt applied the Prepositional-Proposition Theorem to his fortune cookie saying and announced “Your talents will be recognized and you will be rewarded...in bed.” Unfortunately, his date Jill was not impressed.