Sometimes it helps to feel bad for the person rather than get angry. As Gandalf said in the LOTR:

“Frodo: ‘It’s a pity Bilbo didn’t kill Gollum when he had the chance.’
Gandalf: 'Pity? It’s pity that stayed Bilbo’s hand. Many that live deserve death. Some that die deserve life. Can you give it to them, Frodo? Do not be too eager to deal out death in judgment.”

Remember that plumber earns his livelihood on his professional reputation. If he cannot keep an appointment, he is failing at his career.