Northeast dialect, now widely understood. CC-CEDICT notes the variant 墨迹 (mòjì) — same sound, interchangeable spelling online. Implies irritating slowness, not just being careful.
mistakes
叽 here is toneless (neutral tone). Don't confuse with 磨蹭 (móceng), a near-synonym from standard Mandarin — 磨叽 feels more earthy and complaining.
