Practiced by many at many different levels of expertise, but very few achieve true mastery of demanding sport. Great skill is needed to be both immersed in a TV show/film whilst also multi-tabbing Facebook, eBay and Youtube.
Considered a hobby by most enthusiasts, also known as DSAs (Dual Screen Artists). Like any hobby, specific times are set aside for Dual Screening, and can be practiced for long periods by veterans.
When in this state the DSA is unreachable by other humans, and will not respond to any attempts at communication or other worldly distractions.
Guy 2: Nah sorry dude, I'm dual screening tonight, I'm gonna watch Wedding Crashers again whilst skyping my cousin, writing an essay on the first world war and watching kitten videos!
Guy 1: ... Tosser.
Girl 1: Hey baby... I'm feeling randy. Can I come over??? ;)
Guy 1: Kk
Girl 1: Are you dual screening again?!?!
Guy 1: No
Girl 1: Ok well I'm coming ove-
Guy 1: OMG BRUCE WILLIS WAS DEAD ALL ALONG
Guy 2: Hey bro get off the fucking couch! Let's go on a pussy patrol!
Girl 1: Don't even bother. He's dual-screening... he'll be gone for at least another hour.
Some of the more talented Dual Screeners make following their commentary more entertaining than watching the real thing.
Person 2: Nah, I follow this guy on twitter who'll be dual screening it - I'll just read that.