Verb, to point out a diss in an unusually obnoxious and uncalled for manner. There are many ways to present the zing, the most common where you flick your fingers outward in the direction of the person being zinged, and shouting ZING. Other specialty zings include the sniper zing and the predator missile zing.
Liam: Wow these bio notes are way too hard.
Ben: Maybe that's cuz ur stupid and a scrub. ZING.