There used to be a vicious old Boxer dog on my round. He lived at the end of a long drive with a gate. There was a post box outside where I used to leave the mail. Occasionally the owners forgot to close the gate and left the dog out. It would spot me as I was parking my bike, and begin padding in my direction, head down, growling, until it got close enough to launch itself at me.
From the LRB blog. Read more here.