I'm having trouble translating the expression pechofrío (pecho frío, ‘cold chest’) from Spanish—specially Argentinian Spanish, I don't know if it's used in other countries. It means:
s. masc. Persona sin sangre, que no muestra interés, brío ni entusiasmo en las situaciones en las que se requiere. Proviene de pecho + frío, por la idea de que esas personas no tienen el ardor en el pecho propio del entusiasmo. Ej.: Muchos tachan a Messi de pechofrío.
n. masc. A person ‘without blood’ who doesn't show any interest, brio or enthusiasm in situations where they are required. The word comes from ‘cold’ + ‘chest’ due to the belief that these individuals don't feel any ardor on their chest characteristic of enthusiasm. E.g.: A lot of people brand Messi as a ‘coldchest’?
The expression was used mainly in football contexts, but nowadays, people tend to use it in every informal situation—for someone who performs poorly in any kind of activity because can't engage enough.
I only found fainthearted (and could also consider coward depending on the context); but as I looked some examples I found these kind of terms are rather formal. Is this true? I'm looking for an idiomatic or slang expression that would suit in a (very) informal situation. With this sense, if I'm angry because a fellow are just not putting all the effort they should then I would say in Spanish: ‘¡No seas pechofrío!’. But if for example I complained ‘Don't be a fainthearted!’, would this sound too prude? Would my listener laugh and not take me seriously, thinking that I'm not ‘streetwise’? Is there some good idiomatic expression or word I could say in these kind of situations? What do you think about it?