Partner in Crime - I'm so gonna steal that one to describe relationships. The best friends I have, have that magic combination of serious, thought-provoking discussions and sarcastic, silly humour. I'm lucky to have multiple people like that in my friend groups, but not many of them are female. Partner in crime sounds like the best kind of relationship, really: working together to achieve goals, but knowing each other well enough to help the other out.Partner In Crime is a good way of putting it. I have plenty of guy friends who fit that description, but for friends I'm not always certain it's a good thing. For example, I have a good friend like that and sometimes we'd just feed off each other until we'd created a perfect storm of What Not To Do. Live and learn.