In Hawaii, people hug and kiss all the time as a greeting. So unless the kiss occurs outside of the hi, or goodbye, it isn't obvious if there's something else going on.
Depends, if it's a lip lock kiss, I exit stage left.
If it's a greeting on the cheek, then I just go along with it. If it is someone that makes me uncomfortable, then I bring it up later on when we can discuss it calmly