The act of ignoring a phone call from an annoying caller after very few rings, aka hitting the "f-you" button. The term is rooted out of the fact that many popular mobile phone models have a sidebar button to ignore/silence calls.
"Dude, I called you last night and you sidebarred me after 2 rings. Wtf?"
"Omg Kelly... this douchebag just called me and I sidebarred him for the third time this week. Why can't he get that I'm just not that into him?!"
To become sidetracked while browsing YouTube or another video site, usually resulting in forgetting why you were there in the first place and getting mired for hours in a maze of videos that are (or simply looked like they ought to be) funny or enticing.
The other night I was looking for a movie about that new helicopter, but I got completely sidebarred and before I knew it, I found myself watching Coming of Age clips and nearly three hours of my life had just disappeared.