Not a silly question at all! I believe dogs and even cats can act out of spite. I've seen it with our animals. Peeing on something that belongs to their owner is a classic and most common example... eg. My cat used to sleep in my bed, I had to put a stop to this once I gave birth. Shadow displayed his unhappiness by peeing in my room. That cat NEVER messed in the house before! Similar things have happened with our dogs...