When I say I have a boyfriend, why do guys STILL hit on me?

why is it that when I saw I have a boyfriend, guys STILL hit on me. I don't say that ALL guys do this, I just say that and from experience that when I say I am in a relationship right now, they still keep trying? Why don't they get the point? or do I have to say 'I do not want to be with you'? what would you say to get a guy to stop hitting on you? I just ignore past some point. thankx
When I say I have a boyfriend, why do guys STILL hit on me?
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