Basically, we go through the alphabet and give a sexual reference to each letter. (not sure if this game will work, but there we go).
Eg,
Poster 1: A is for... anal.
Poster 2: B is for... boobs.
Poster 3: C is for... cunnilingus.
And so on and so forth.
So, I'll start.
A is for... aphrodisiac