Man Rule

[Nomad]

OK, I know it is forbidden to date the sisters, exes or potentials of your friends, but, seriously...
How wrong would it be for me to date my buddy's sister?

Why not ask him? If he freaks out, you might want to rethink it... but he might be fine with it. As someone mentioned, don't share details though...

 

[mmartist]

I don’t think there will be a problem dating her. You should probably be more careful when it comes to some aspects of the relationship but I don’t believe this will be difficult.

 

[Gentle Fist]

I would also say its fair game... Just know that your friendship with him could go away following a bad ending to the relationship with her.