My sister and I have a fairly love hate relationship. Went out for dinner last night and each paid for what we had (it came to about 70 altogether). As I went to pay my share (significantly more), she queried the bill and asked the waitress for a couple of more minutes to pay hers.
Incidentally they had left my cocktail off the bill which she was furious about and insisted I should still pay for. The service was appalling and the meal was very average and overpriced so as far as I was concerned it was fine. But no, she mentioned this to waitress in order to get me to pay it! 
She then made as if to leave the restaurant, thereby saddling me with her portion of the meal! 35 quid extra for me! And the cocktail... She only stayed when the waitress saw and came bustling back over.
This left her in the position of paying not obly her share but also for my extra cocktail - karma?
(She is currently forcing me to give her the money...)