Anyone heard of "Sev Trek"? Cartoon parody site of Star Trek (and other sci-fi stuff). A scene is set with a context, but the final frame (or final speech bubble if a single frame toon) is left blank and you enter your thoughts on what the killer line should be.
Great scene, for example, of an away team battling some alien monster or other, Picard, Riker, Worf, Data, a few redshirtensigns.....Picard says, "Fire at will!"
Riker says, "Yikes!"