Gentlemen in the crowd, don't act so surprised. If there are rules in dating when it comes to guys, there are obviously rules for us girls as well.

One of the major commandments? THOU SHALL NOT STEAL YOUR BEST FRIEND'S BOYFRIEND.

Or in this case, ex-boyfriend. But just like how men would have the decency not to move in on his best friend's ex-girlfriend, women have those inhibitions as well. Though given time, the parties involved would eventually forget and move on.

However, poor Kristen. It hasn't even been that long when she and Rob broke up when rumors got back to her about her pal Katy Perry and her ex hooking up. Talk about betrayal from both sides.

In Katy's defense however, she publicly stated that nothing happened. She didn't break any girl code and she wasn't dating Kristen's man (ex-man, whatever). She said that she didn't want to disrespect Kristen at all.

Kudos to Katy for taking initiative to clear up the rumors!