Just jumping in to clarify it for you, as you can really only tell what triggers it by decompiling the game, but it's basically Cnt. If you get that value above 3 then the exhibitionist text will trigger at the end of the public noticing you mini-scene. What it tracks is the number of times the public has noticed you having sex (or some other similar action) in public, and if the scene ends it will reset.
As for the rest (just for those curious), D20 is a dice roll for randomness, used in this case to check if the other girls notice what you are doing; HolderCount is used in the stat notifications; Player.Focus is how close you are to cumming; and Round is the remaining time before time advances to the next period.
