I'm not sure how fancy a solution you were looking for, but here is a simple way to get a reminder in Excel.

Put the date you need the reminder into a (hidden) cell.  Name the cell "ticklerdate".

 Somewhere front and center of your spreadsheet, put a big (maybe merged) cell with white font so it doesn't show, "Remember my wife's birthday!!"

Then set up conditional formatting such that when today()>=ticklerdate, the format of the cell goes to black print on neon yellow background and font size goes to 24+.  That'll get your attention.