The outer labia of the ladybits. Also a good insult for someone who is utterly useless.
"look at the state of you ya twatflap!"
by Slimbun September 08, 2006
The flap of a woman's vagina. A derogatory word to call somebody who is pissing you off.
"Shut your fucking mouth, you stupid twat flap!"
by Kizzle82 May 11, 2007