Meeting old friend's fiance for the first time (they had been living overseas) at their new house.
Conversation was all normal, the usual, polite, friendly etc.
When my friend was out of the room I asked her if she'd made the cakes herself (just making conversation really) and her face darkened to a hard snarl.
She then (and I still struggle to believe this actually happened) shoved her face up close to mine and said 'Of course I didn't fucking make them myself, what a stupid fucking question to ask you stupid fucking cunt'.
I was 
Then she called me a stupid slag.
When friend came back into the room it was as if nothing had happened.
Still in shock, I made my excuses and left.
The next time I met her, in the pub with a group of friends, she was all sweetness and light to me, until several drinks in she started with the stupid fucking cunt routine again.
I now avoid her (and sadly, him) like the plague. Though there's a mutual friend's wedding next year that should be interesting... 