1) Guitar Hero activity 
verbally bantering with the audience.
A term from jazz, derived from 'refrain.' A musical riff is a creative improvisation on a partiular phrase. More generally, riffing is performance characterized by rapid, energetic improvisation, whether verbal, physical, or with a prop.
verbally bantering with the audience; also know as crowd work.
Improvised interaction with the audience. Often used by MCs to warm up a crowd, or for comics performing longer sets to modify the energy level of the room. It is also worth noting that riffing creates a strong humorous reaction by using current events, see this previous post on the topic.