Dead as a doornail

I'm Jack Cade. I'm pretty devious and I'm always looking for a way to outmaneuver people. Hey, the more violence, the better. And you know what I think?

Brave thee! Ay, by the best blood that ever was
broached, and beard thee too. Look on me well: I
have eat no meat these five days; yet, come thou and
thy five men, and if I do not leave you all as dead
as a doornail, I pray God I may never eat grass more. (4.10.35-39)