Anyone who another person feels superior to. Not as good at someone in pvp, you're a scrub. Not as good at someone in PVE, you're a scrub. Cheese the boss, you're a scrub. Didn't cheese the boss, you're a scrub. Got exotica from Xûr, you're a scrub. Got exotics through random chance, you're a scrub. Like Halo/CoD/Skyrim/Fallout, you're a scrub. Have/don't have a significant other, you're a scrub. Call someone a scrub, you're probably a scrub.