My friend Lesley and I have at least one thing in common: a very inappropriate sense of humour. We laugh as hard and as often as possible, quite often at the most inopportune moments.
Once, in a free meditation session at work designed to de-stress, we were doing neck stretches, turning our heads slowly side to side. We managed to face each other only once and as soon as we made eye contact we were away. We were asked more than once to stop laughing, but it was useless - I couldn't get the picture of her suppressed laughter out of my head. The snorts were unstoppable.
The 'out of order' attitude extends to our nicknames for each other: she's the Old Tart, and I'm the Tartlette. Some might be offended by these name tags, but I guess we're pretty assured of our affection for each other (either that, or we've both accepted the fact we're tarts and have moved on).