I thought this was a ridiculous reg at first as well. I had never heard of anything called "Sweetest Day" before but I googled it and it does exist. Sweetest Day gets 22,000 exacts and celebrate is a logical word to go with it. However, it can't be compared to 'Christmas' which gets over 2.5 million searches per month
Eventhough the wording as it turns out does make sense, I think it'll have to be one that you develop if you want to recoup more than your reg fee.