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Harmless sentiment or thoughtless insult?

Justin Timberlake is in hot water on social media for using an "n" word -- but not the "n" word -- in a birthday message to Madonna. But his critics say his choice of the word "ninja" was too close for comfort.

"A HAPPIEST of Bdays to my mother chucking ninja, @Madonna," Timberlake tweeted to his friend the Queen of Pop on Aug. 16. "Hope you have a great one, M!"

Then, as his critics pounced, Timberlake deleted the tweet many deemed offensive. "'Ninja' is commonly used as an alternate word to [the racial slur]," explained a post on Consequence of Sound, which also shared a sampling of posts from Twitter users pointing out the singer's perceived misdeed. "I knew Justin Timberlake was getting too close for comfort with black culture but now he is saying ninja. #nosir," wrote one user.

Another website that reported on the story, The Hot Hits, implied Timberlake should have known better than to use the word. "Before you shout out, 'BUT HE SAID NINJA! STOP OVERREACTING!' you should know it's not uncommon in America for those who think they're smart to use 'ninja' in place of the other word, as the Twitter users up the top have caught," wrote The Hot Hits.

What do you think of Timberlake's message to Madonna?