Theater Lean is where the screen before the previews comes up telling everyone to shut off their cell phones so there are no disruptions during the movie.
Keep in mind, movie theaters provide tight seating, and cell phones in front pockets aren't easy to access.
At this point, most moviegoers will lean the bottom half of their body to the left (or to the right, depending on which pocket the phone is located in) so there is easier access to the phone. They will keep their body in the leaning position while they silence or shut their phones off.
The phone will then be placed bakc into the pocket, and the moviegoer is free to get out of the leaning position and enjoy the movie.
Theater Lean can also be used to access a cell phone in your pocket while driving a vehicle, sitting in a desk chair, or in any other situation where you are seated in tight quarters.
Watch this, when the screen turns on, I bet half of the people in the theather will partake of Theater Lean
*3/4 of theater partakes of Theater Lean*
Whoa! That was a ton of Theater Lean!
*Phone goes off in pocket while driving*
Oh dude how am I going to get my phone out of my pocket?!
Dude partake of the Theater Lean, it'll be a cinch
*Partakes in Theater Lean*
Oh wow, you were right, that was so easy! I love Theater Lean!