Knees together?

Something one forgets is how you sit actually matters depending  on what you're wearing although it's fair to say boys (and men) tend often to sit with their legs spread well apart.

For those of of us who wear skirts and dresses it's different in that  if we do, then we're flashing our knickers which is regarded as being very rude and even embarrassing in the presence of boys.
Sometimes I rather forget myself about this and would like someone to work with me on automatically keeping my knees together from the minute I sit down in company.