Does "running at both ends" mean vomit and diarrhea at the same time? Is this a common usage? I can't find this usage in the dictionary.
I read this from the book Dirty Chinese. I doubt its correctness, so I opened this question to confirm.
Man, that poor bastard has got no luck at all. Between the booze and the diarrhea, he's running at both ends.
This is figurative language, used for effect. It's not a very common idiom or well known phrase. It does mean, in context, that he has diarrhoea and is vomiting. For example, here is another use of the expression.
The use of "running" to mean "allowing a liquid to flow" is standard. "I left the tap running." And this is just a development of that meaning - with the intent of creating a phrase that is grotesque, funny, and impactful.
This may be a literal translation of the Chinese idiom, or at least an attempt to preserve some of the flavour of the Chinese - this book is for English speakers learning Chinese, not for Chinese speakers learning English. It's correct, meaningful and understandable in English.
