Is it normal my friend thinks kissing is gross?

I think that a large portion depends on cultural/ethnic backgrounds and on how a person was raised as a kid.

For instance, some abused people think that sex and other things related to it are "gross" or "wrong" due to the things they've experienced. Though, this doesn't have to mean that your friend was or is being a abused.

I personally am disturbed by relatives kissing each other on the mouths. I think it has to do with the fact that I sexually abused as a kid and kissing or attempted kissing on the mouth, was one of the methods implemented.