Entry to America for an Irish person on the 90 day visa?

Question

If an Irish person comes back to Ireland from america before the 90 days are up, how soon can the person go back to america and use the 90 day visa again

Answer 1

As  long as your passport gets stamped in Ireland, you can fly back to the states the same day and get a fresh stamp in the U.S.

I'm fairly sure this only applies to EU countries and not to Canada or Mexico because it is a heck of a lot easier to just pass over into Canada or Mexico and then come back.