[thaumasiotes]

I'm not sure I can really speak to how the "average person from the US" would deal with 2015-04-03, but two data points:

1. Everyone I personally know would know that that meant 4/3.

2. 4/3 in US usage is April 3rd. As I understand it, it's March 4th in European usage, but you say they have no problem with YYYY-MM-DD. I tend to suspect that you sort of half-learned that "US dates are backwards from European dates" and then misapplied that lesson here.

[iSnow]

> As I understand it, it's March 4th in European usage

British usage. For Germans, 4/3 means 1.33333. April 3rd is 3.4. here. If you do i18n, do NOT assume there is one consistent European convention. Either use ISO 8601 or a library that understands country conventions.

[DanBC]

I wouldn't assume anything if I saw 4/3.

4/3/yyyy would be day month year.

People probably say "Tuesday the 3rd of April, 2015" instead of "Tuesday April the Third, 2015".

(Brit here.)