I didn't wear a costume today but did yesterday - Luna Lovegood from Harry Potter:
At final count, I had spotted 52 girls/women dressed as Harley Quinn. Probably 3/4 of them were dressed as the more recent iteration of Harley Quinn (shorts, Daddy's Lil Monster t-shirt, etc.) and the rest in the previous iteration (black and red outfit). And 5 were probably too young to be wearing such an outfit - I'm being very conservative here; since I know many people look young for their age, I counted "too young" as anyone who looked under the age of 12. Perhaps Harley Quinn is the new Slave Leia?