best friends ex, should I? Options

[potatoespies]

My best friend is in a new relationship and I asked her if it would be okay if I pursued anything with her exboyfriend.
She said it was fine.
They only dated for a month a year ago and now they're really great friends, so I feel like it's okay.
But there's the rule of "never date a friends ex" so I'm scared.
Especially 'cause when she gets in a bad mood she'll laugh and joke about getting back with him (even though she hated dating him, she was too mellow for his craziness).

Should I pursue anything?
I don't want to make her feel bad, but I really do like him.

[Melissa]

If she only dated him for a month a year ago, then it doesn't seem like it was ever serious. What I think is bitchy is that she would joke about getting with him when she's feeling crabby.

I would go for it. There's no such thing as best friends, anyways.

[fameONE]

I would go for it. There's no such thing as best friends, anyways.

That says a lot about you.

[Melissa]

That says a lot about you.

Not really, except for the fact that I've had a so-called best friend stab me in the back and therefore don't care much for the entire idea of "best friend" anymore. If that's what you got from what I said, then yeah, I guess you're right and it says a lot about me.

Besides that, why shouldn't she go for it? Liking and being with a guy isn't this whole idealistic thing with exact rules and clear-cut boundaries. Sure, you generally don't go after your friend's ex, but this guy was with her best friend for ONE MONTH. That's pretty minuscule. It's not like she can completely control what she feels towards this guy and it isn't like she didn't ASK her friend if it was okay. I think it's a pretty bitchy thing for her friend to keep holding on to whatever scrap of relationship she had with this guy to swing in front of her whenever she gets a bit pissy. It's like... okay, you guys tried, you guys didn't work out, it's been a year, it's about time to move on.