splenetic — bad-tempered, spiteful, or irritable

a red-faced customer slams their fist on the counter while pointing aggressively at the barista. Their mouth is wide open in an angry shout with visible frustration lines radiating from their head. The customer's aggressive outburst was triggered by having to wait an extra minute for their coffee order. The barista steps back with a shocked expression while other customers turn to stare uncomfortably. Several people in line behind the angry customer look annoyed and embarrassed by the inappropriate reaction. Other patrons shake their heads at the unreasonable display of temper over such a minor inconvenience. someone being bad-tempered, spiteful, and irritable over a trivial situation