The phrase may describe someone's general attitude, not just a momentary mood.

Context Matters

It doesn't always mean a literal fight, but can refer to any argument or conflict.

Metaphoric Use

Often implies that the person is not just willing, but eager to argue.

Usually implies readiness for a physical altercation, not just verbal.

It suggests the person is acting in a way that could provoke a fight.

Body language, like clenched fists, often accompanies someone spoiling for a fight.