Well, that'd have to be a pretty small unicorn for me to be able to leap-frog over it well enough for the obvious threat to come into play in the first place. (I.e., if there weren't that horn there, I think it'd still be a humiliating exercise for me regardless.)
As for tap-dancing ... hmm. That's not usually an activity where I would want to be very close to another tap-dancer anyway (hooves, horn, or no), simply going by my observation that all the famous tap-dancers I can think of end up doing a lot of wild kicks and swings and so forth as part of the routine. Well, and that I don't know HOW to tap-dance, so, again, just another recipe for humiliating failure.