I thought that 'irascible' had a connotation of stubborn, rather than just easily angered. To contrast with cantankerous -- cantankerous is angry, but irascible has principles. Or something. But according to Dictionary.com, that's not the case; irascible is just as arbitrary as cantankerous.
Once upon a time, there was a very bad-natured lion. She was angry because she was in pain, and she was in pain because there was a thorn stuck in her paw.
A clever mouse, who had read enough fables to know how this one ends, approached the lion cautiously and said “I’ll remove the thorn from your paw, if you agree not to eat me!”
The lion scowled, and snarled, but finally nodded her head, and the mouse made quick work of the splinter.
“Now we should be fast friends,” declared the mouse.
The lion yawned, and ate him.