Well, since you're an ungrateful little wretch who's reading The Blog of Days, we'll indulge you: May 12 is the birthday of Florence Nightengale and (not coincidentally) the end and culmination of National Nurses Week. If any of the mothers in your life are nurses, you can combine these two celebrations and perhaps earn some brownie points as well.
Usual Suspect Days of the Year mentions that Sunday is Doodle Day. If you have kids at home, perhaps they can surprise Mom on Sunday with their best doodles. Homemade cards are often much appreciated; they are not (necessarily) proof that you're just a cheap bastard.
Sunday, May 12 will also be Limerick Day, commemorating the 201st birthday of Edward Lear, the English poet and artist who popularized the limerick (and, according to legend never once tried to rhyme Nantucket....)
Lear was also the author of such children's classics as "The Owl and the Pussycat." Surely you remember your mother reading that to you as a child:
Now, stop this nonsense and plan to call your mother Sunday. If you still can.They dined on mince, and slices of quince
Which they ate with a runcible spoon;And hand in hand, on the edge of the sand,
They danced by the light of the moon,They danced by the light of the moon.The moon,