For me a kiss is signification of promise and trust. I don't like to be in close proximity to people unless I trust them. There are some kinds of kisses (a quick kiss on the cheek) that I would give and receive from family members and significant other that means "Don't forget that I care about you." If I were to kiss someone that I don't care about it in the way appropriate to that classification of kiss that would feel like a lie to me. And sometimes, also, the idea of kissing just strikes me as ridiculously gross.