Como dizer "ter sangue de barata" em Inglês?

I was watching TV the other day when one of the characters in a soapopera said: eu não tenho sangue de barata. That made me wonder how we say that in English. Do you have any idea? If not, keep reading. Here's what was going on in the soapopera when that expression came up: A man was really mad because some people were ploting against him thinking that he would never react to their provocations or that he's too scared to fight. When you're in a situation like that, you can say "you're not milk and mild". Let's think of a different example.

Imagine your boss treats you badly in front of your coworkers. He yells at you, makes you do things that's not part of your job and even teases the way you act, speak and work. He's definetely crossed the line. While you're talking to one of your coworkers about it, who's also a close friend of yours, he tries to open your eyes and make you stand up for your. Here's what he says: I don't think you should put up with the humiliations just because he's your boss. I know you need this job, but prove him you're not milk and and mild!" About the vocabulary in the expression, mild refers to someone very gentle, softhearted, calm and gentle. Those are actually all synonymous with mild. As for milk, that can be an analogy with the way a gentle person is: smooth and soft. That's it for today guys. Take care!