Difficult to know what to say when you suddenly find that you are talking to a complete Knucklehead.
Could try :
"Sure, Harley is the only bike worth owning, if you want to impress other Harley owners."
And if courageous enough, you could add (with a shrug) :
"But if you don't really care about their opinions, then you'll find a lot more bikes to choose from."
Though even that's getting uncomfortably close to The Customer Is Wrong.
Obviously this guy owns some major bad Karma from the past . . . otherwise he would have been born with a brain from higher up the Evolution Tree.
Charitably, you can hope his next re-incarnation turns out better.