Other contributors have said "What do you feel on April fools day?" is the same question as "What do you feel on April Fools' Day?" If you believe that these are not asking the same thing and should be answered differently, click here
That's when you greet someone on April Fool's Day. It's like saying "Merry Christmas". Your just happy!(Since it's April Fool's Day, give them a little pinch goodbye if they are not wearing green!)