I deliberately didn't sign up for my workplace birthday planning calendar. I chipped in for others birthdays but didn't feel any need to get my turn. So they made mine April 1st.
Ours was kept in a Microsoft Word file, so there was no automatic error checking. For years, I got away with telling them it was "February 30th." I'd rattle it off so easily, no one questioned it. We got a new admin assistant who caught it and then went through personnel files to put the list together.
Actually, I told them to take my name out or I'd file a complaint about going through personnel files and extracting birthday information as a privacy issue. (When that was done, they wrote down the year, as well.)
When i used to visit online forums, all of them made you register and put in your birthday. I think April 1st was the easiest date to choose. So every April 1st, I used to get tons of emails from forums telling me Happy Birthday.
Touché.