Is my friend choosing the wrong path?

i have this friend and she has been acting different lately and its not a good thing. she has been talking all gangsta lately and she is normally a classy young lady. she has been talking to this boy who is a year older than her. he is really bad kid. he does drugs and gets into fights and he is always in trouble at school. he also is sex crazy with girls. i am afraid that's all he wants her for but she doesn't agree. my and my other friend have tried talking to her about this but she denies everything. she is gonna ruin her life. this would be her first bf so i think she just likes the fact that someone likes her. i just want her to find a nice clean guy but she wont listen. what should i do?