Wearing black and brown together: it's just against 'the rules'... or used to be. A lot of fashion faux pas have been debunked recently, like socks with sandals and denim on denim. I smell a new blog post series in the making.
As with all apparent faux pas, it's all about how you style it. It may feel weird mixing two base colours, but the trick is to treat the brown as if it's red or orange or anything but a base colour.
Items of clothing with both brown and black in them do half the work of mixing these two seemingly immiscible colours together in an outfit. The most obvious examples are animal prints like leopard or giraffe, though I am personally not a fan of animal prints.