Assuming that this isn't just all made up for some evening drama, it's hard to envision how this went down from the details provided. The likeliest two ways I can see it was a socially maladept guy who meant it as a playful pat on the butt, the way some people might ruffle a baby's hair or tweak their cheek (not appropriate for a stranger, but like I said if they're socially maladept)...or if it was a serious spank, then it's someone suffering from some sort of serious mental illness or impairment. Either way, Ghost's response would suggest he's unable to exercise rational control over his actions, and poses a threat to society requiring isolation from the public, and/or he's also suffering from serious mental illness or impairment.
But being GFY, he probably just made the whole thing up to get some attention and stupid banter going. It worked.
