Mr. Knightly is a rancorous old man who is always unhappy and seemingly angry at everyone, even if they are strangers.

You could say that someone who is always angry and irritable is a rancorous individual, though you might not want to say that to their face.

I tend to be very rancorous in the morning, when people try to wake me up before it is necessary and I could have slept a little longer.

While most dogs are friendly and sweet, they can become rancorous if they are treated very poorly, going so far as to resent all humans for the actions of one.

The boy I met at school today was a transfer student from abroad, but he was so unhappy with leaving his country that he was rancorous and unfriendly to everyone.