Something nasty
Something nasty is an suggestions excercise.
The ref suggests a topic that is perverted, racist, insensitive or otherwise inappropriate for any but the most awkward scene. Improvisers then perform a scene, interpreting the suggestion in some non-offensive manner.
This exercise helps actors deal with inevitable poor audience suggestions. In one show, actors responed to the suggestion of "rapegasm" with a scene about a roller coaster called the Rapegam.