Is there a guidebook for the Wingman?

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My girlfriend has had horrible luck with dating the last year and a half. She is now trying to meet someone online and wants my help. she has asked me to meet the guy iwth her at whatever restaurant they choose. I tried to tell her that meeting him in a public place was good......she should just let someone know the details of who she is with and where they are going in case he does turn out to be a wierdo. she still wants me to be there. So, I was just curious......are there some lines that your wingman doesn't need to cross?