Last week, a neighbour kissed my baby on his lips. I was so surprised, I didn't even respond. I think it's unhygienic and disgusting. Am I overreacting? How can I be polite, but make sure this doesn't happen again?

You're not over reacting! It is possible to be straight with this person without offending them. Just tell them you believe it is unhygienic and it's your right as a parent to stop someone from doing something to your child that makes you feel uncomfortable.