Both NationalDayCalendar.com and HolidayInsights.com offer clickable lists of funny national days. Both sites offer monthly lists of funny national days, and clicking on a particular month pulls up the funny days in that month.
For example, clicking on the June link from the NationalDayCalender.com home page links to a list of days with the national days beneath it, ranging from National Heimlich Maneuver Day and National Go Barefoot Day on June 1 to National Martini Day and National Flip Day on June 19.
On HolidayInsights.com, the setup is much the same. Visitors click on a particular month to see holidays, special and wacky days for that month. For instance, clicking on December brings up information about Eat a Red Apple Day, which is observed on December 1, and National Fruitcake Day, which falls on December 27.