I would give Closer a 15 rating. Reason being that the language is strong, but its used in a particular enviroment. The sexual language is very common but its used within the conversation. There is anger shown by the male who you expect to dominate the woman, this could include promoting physical violence upon women.
I would give this film an 18 rating. The gang culture is intimmidating towards us viewers and they are shown mugging and also smoking drugs. There is also an incident where a woman with a push pram is shot by two of them on a bike, which is also illegal on public footpaths, we also have a POV of this which makes us feel in the action and responsible.