Person, usually a teenager, who engages in sexual (sinful) activities in the movie theatre or "cinema;" therefore he or she is a "cinner" spelled with a 'c'.
Also as a verb, ex: We were cinning the entire movie once we realized we were much more interested in fulfilling our hormone-raged feelings for each other than watching the movie for which we paid $8 to see. I want to cin with you.
16-year-old girl: Brian and I moved to the row of seats in the back of the theatre so we could make out without being in anyone's direct view. I gave Brian head while we were at a movie. We cinned at the movie, then drove around to find a dark corner of a parking lot in which to have some hot car sex.