You'd think she'd be used to them by now.

Britney Spears was celebrating her 30th birthday with friends and family. including her sons Sean Preston, 6, and Jayden James, 5. Well-wishes from her showbiz friends poured in, including greetings from Rihanna, Christina Aguilera, Katy Perry and others. But an uncensored video message from Ke$ha quickly changed the mood from celebratory to awkward.

In the message, Ke$ha sent a message of congratulations, ending with "Happy f***ing birthday!", prompting demands of an explanation from the boys.

A red-faced Spears later tweeted to Ke$ha,  "Thanks Miss Kesha. Just watched this in bed w my boys. Now I have to explain what F---ing means!! U rock Xxoo."