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1.
To carelessly get pregnant, drink excessively, and not take care of your children to the extent that you end up losing custody of them.
Sherri had everything going for her until she decided to start doin the Britney.
by Jaylou December 22, 2007
 
2.
It's when you see someone dancing and singing along to a song but you can't hear them singing. Usually done at traffic lights when people don't know that they're being watched. It's lipsyncing in reverse. Named after a performer who is renowned lipsyncing and dancing to her songs.
I was stopped at the traffic lights and this chic pulled up behind me. I looked in the rearview and she was Doin' the Britney, She was grooving about, waving her hands and singing to a song. I couldn't help but have a good laugh.
by Dirtyhound November 15, 2009