Back in the home country, it is normal to kiss each other on the cheek three times (left, right and left again). You kiss when you see people you’ve met before (family, friends, and sometimes colleagues), you kiss when it’s people’s birthdays and to wish each other Happy New Year. Men kiss women, women kiss women but men only kiss men in certain circles (not necessarily just gay men, also good friends or fathers and sons). Really good friends hug each other or kiss each other only once instead of three times (which is why I think hugging is way more intimate than kissing each other on the cheek, I assume the average American will disagree). In other European countries people only kiss each other twice, which makes for an awkward kiss in the air when you’re used to kissing someone three times.
In the US it gets even more complicated, because here people hug each other instead of kiss. That makes for a very awkward make-out-like situation when you’re used to kissing people but instead you’re supposed to hug people. And it took me a while to find out that there is certain etiquette to this polite hug that Americans give each other. Always on the left side of the other so that your right hand can pat on their back, and not too much body contact, even though I thought that was the whole point of hugging someone.
It becomes even more complicated with European or South American friends here in the US; do you kiss each other like back home (and then do you kiss twice or three times?) or do you hug each other like in the US? Anyway, lots of awkward moments to be had.