Put delicately, I have what one might call a “highly developed sense of personal space.”
Put casually, I don’t like feeling crowded.
Put bluntly, don’t touch me unless I know you extremely well . . . and maybe not even then.
Mind you, I also have a fairly well-developed sense of politeness (if only so I can ignore it when I so choose), so I can shake hands with a smile, and have adapted fairly well to the South Florida custom of hugs and cheek kisses.
Sometimes it’s more effort than others though.