Phone Sniper
Someone who constantly watches their phone, waiting for a text or social media update to pop up in which they'll like and/or comment within seconds. The only time a Phone Sniper doesn't text back immediately is when he/she doesn't want to.
Dude: Hey
(Seconds later)
Phone Sniper: Hey
Dude: That was fast, you phone sniping me?
(Seconds later)
Phone Sniper: Hey
Dude: That was fast, you phone sniping me?