It's fair to say that the French kiss a lot more than most other nationalities. You kiss people hello and goodbye. Leaving a large gathering first can take hours, as you lean across tables trying to find one cheek and then the other*.
When I first started visiting France on a regular basis (before I actually lived here), I was a bit weirded out, but quickly figured out generally how it worked.
1) Everybody kisses children
2) Very small children tend to get one kiss on the head or cheek rather than the double-tap everybody else receives**
3) Women kiss everybody
4) Men kiss all women
5) Men kiss all family members
6) Unrelated men shake hands
7) Don't hug anybody***
This was my system and it worked. It worked flawlessly. And for me, not being related to anybody over here, it essentially boiled down to "Kiss women and children, shake hands with all men".
It worked flawlessly until recently, when a man went for a quick peck on the cheek. It was awkward, as I'd stuck my hand out. So he apologised, and we shook hands, and then proceeded to find important things to do elsewhere. I thought this was just a one time slip, a French person getting confused due to tiredness or distraction.
But no! The next time we met, it happened again. And the time after that he greeted his girlfriend's brother with a kiss. I've seen these two shake hands hello before. And he doesn't kiss his girlfriend's dad. And even more confusingly: They shook hands good bye.
There's another level of break down where you kiss hello and shake goodbye. An entire layer of this interaction I'd been missing. I might have been being super rude to people for the last couple of years and nobody has told me.
Now that I've found this mystery, I'm damn well going to get to the bottom of it.
*The system works by kissing the left cheek then the right. Sometimes you just kind of kiss the air, sometimes you make contact. This just seems to be unimportant and just depends on how you are standing. Never go right first, you'll end up kissing on the lips. You don't want to accidentally kiss your girlfriend's mum like that.
**This is largely as kids as twitchy little buggers and sometimes you're going for a cheek and accidentally end up kissing a three year old on the lips. Then you are sent to prison FOREVER.
***Hugging is just for couples. I like this; It means I get my revenge on my girlfriend when she visits the UK and my parents will hug her.