irascible
Easily angered and quick to get mad over little things.
Irascible means easily angered or quick to lose your temper. An irascible person gets irritated by small things that others might brush off. If your normally patient math teacher becomes irascible when students forget their homework for the third day in a row, he's reached his limit and starts snapping at people.
The word describes someone whose anger flares up quickly, like a match that strikes easily. You might read about an irascible old hermit in a story who yells at kids for walking near his property, or know an irascible coach who shouts at players for tiny mistakes.
Being irascible is different from having one bad day or getting reasonably upset about something serious. It's a pattern of overreacting to minor annoyances. The grumpy character in a movie who grumbles at everyone and everything is often portrayed as irascible.
People sometimes become more irascible when they're tired, hungry, or stressed. While everyone gets cranky sometimes, an irascible person lives in that mood most of the time, ready to explode over things that don't really warrant such a strong reaction.