Veamos, por lo menos aquí (españa), decir:
- Siempre que vamos al monte con juan acabamos hechos una mierda, para el arrastre. ( porque va a un ritmo tan fuerte, rápido que nos deja muy cansados)
- Vaya mierda de pelicula que vimos ayer.( porque era muy mala)
- No, a esa playa no vamos que esta hecha una mierda. ( porque esta muy sucia)
- Tu tio eres un mierda!, ( in this case yes is a bad word, but just in this case, becasuse you are refering to a person, and you say this to offend somebody. But not in the above cases).
I suppose Auser that the suppressed word is Pu_ta, but si the same case, this word in all the case hasen´t got the same means, is just if you call it to somebody, because means prostitute, but a movie, or a food or one thing, whatever can´t be a prostitute. I think is important to distinguis them bescvavuse in spain people use a lot this kind of expresions, maybe is for this that people says that spanish from spain is more strong even more bad mannered. However this just an impresion, because the foreing person undestand just one of two means of this word, and we use them with others and diferrent means, the use of this word is extended in spain, and we are not for this bad mannered persons, is just that people got a too strict means of this kind of words.
And mierda and pu_ta are diferrent , notice that you can put in the above sentece the adjetive pu... just before the word "mierda" giving grip to the sentence.
I don´t know if you understand me now, aniway I´ve tried it.
P.d: People that learn a lenguage must consider the coloquiall lenguaje, not omit it but learn to use this kind of words.
Sorry for the mistakes.
Un saludo