A couple of years ago I know a investor who did really well bouncing between being short and long on FNMA.
If I were shorting - I would bet against Cinemark, Regal, AMC...
The millennials are watching movies in different ways such as streaming etc. I read that there were 38 million fewer tickets sold in 2016 than 2015. I think there are several movie studios developing a service where you can watch premiere movies at home.
Or another way to short is to watch what new business Amazon is starting and short stocks in that sector.
I think that Blue Apron was hit pretty hard when Amazon announced it had filed a trademark for meal kits.
Of course I would have shorted Facebook - I thought and to some extent still believe it is just a website.