Thou shalt never bitch about a friend/female relative's boyfriend (even if he is a low-life).
Even if he dumped her for her mother, just nod sympathetically and say "Mmm, you poor thing." While discussing your partner's flaws is acceptable (although your boyfriend might disagree), trashing a friends lover has a disturbing way of coming back to haunt you.

rule2 Thou shalt never meet up with a friend's boyfriend for a coffee/drink/dinner, etc.
Such a meeting will never be seen as an innocent social gathering, even if it really, really was. For instance:"If it's just a coffee, why couldn't you go with Jill/Jackie/your brother?" It's best to discuss the boundaries as a threesome, before things get sticky.

rule3 Thou shalt never, ever go out with a friend's ex-boyfriend, even if she says it's okay.
It's just not that simple. Even if she went out with him 15 years ago, when she was in Year 8, it's still going to get on her nerves. And her snide comments will no doubt get on your's. Alas, it takes two very grown-up women to make this work, and not many of us are up to the challenge.

Your Name:
Your E-Mail: