You are now free to pirate any of Disney's movies, because you mentioned a date in your tweet.

"May the 4th" is a date, a generic term, not trademarked, and you can't claim content as your own just because someone mentions a date in their tweet. Of course we don't actually want you to pirate any of Disney's movies. That would be wrong. But if they use your content in their marketing without your express permission, then morally...