Defining an event or action as a "Saw Cock" implies that said event or action is distinctly unpleasant, much like being brutally ass-raped by a large cock which has a saw structure on the lower portion.
Nick: Are you ready for this Macro final?
Mitch: Hell no, it's going to be a saw cock!
Someone or something that bites your ankles.
To a postman, an ankle biter is often known as a dog.
To an adult, an ankle bitermay be a toddler.
To hikers, an ankle biter is sometimes a tick.
And so on.