The act of stealing your friend's girlfriend (preferably your best friend), keeping her for just 3 weeks, break up with her and a year later, get her back for only 3 months and then break up again.
A term used normally for players with "ranged" attacks in a video game, used when someone is crying (hence the Q.Q face looking like the O.O face with tears) and not doing anything. The phrase "pew pew" is an onomatopoeia for a gun firing.