Okay, ya got me. There really isn't such a day, at least that I know of. I'm guessing Hallmark doesn't have a card for it, as yet. But, besides that, there really should be a Word Play Day. For us as writers, as creatives, word play is fun. So, let's have a bit of fun!
There are some words, some created by advertisers, that really need to go away, though. You've heard me harp on some of these before. Words like 'melty' and 'pre-owned'. Sometimes they take a perfectly good word like 'epic' and Doc Frankenstein it until we're ready to rally the villagers. Please, no more 'epic' movies or movies of 'epic proportions'. Unless it's epic-alicious. Or an epic-palooza. Okay, I'll stop now.
Keep writing, friends...and making up words.