DOB fields that pop out a calendar to choose your DOB on, instead of just letting you enter it manually.
Unless you were born in the last month or two, it takes far more clicks to go back to the year you were born that it would be to just enter the 8 digits of your DOB.
And IMO, the purpose of popping out a calendar when filling out a date is so that you can see what day of the week each date is, both to schedule things, and to remember when a date was. With a DOB, it's not like I'm sitting here filling out a form and being like "I think I was born on a Tuesday sometime in late November, lemme see what the date it was..."
/rant