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?

Definitely not over reacting I think what people are missing here is the fact that the hygiene issue is only part of the problem. Even though most will point out "I don't want people kissing my baby on the lips because it is unsanitary" I think deep down its not the main problem. There is a part of us that cringes when someone takes that kind of liberty by doing something that intimate without your permission. If your neighbor kissed you, you probably wouldn't think oh my god she'll give me germs, it would be more a situation of "That is an action is reserved for people that are really close to me" Anyway I think if it is really an issue of hygiene then you can let it slide, as everybody else has said the baby will put worse things in his mouth, but, if as I suspect, it is the intimacy of the act , you have the right to say please don't do that.