what could he have done to the fat girl´s friends?
Obviously he didn´t kill them, otherwise the fat girl´s reaction would have been something else apart from making a slight fuss. But it´s evident it was something serious and that girl knew quite well the kind of person he was and she confirmed so when he silently insulted her. Rape is not an option because she would have him detained by force to call the police. I think this is another subtle mistake in the writing of the movie.
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