big girl’s blouse Brit. informal
a weak, cowardly, or over-sensitive man.
Big girl's blouse is a phrase that originated in the North of England (a stock line for Northern comedians such as Bernard Manning and Les Dawson) but it now used widely throughout the country.
It is normally used as a term to playfully ridicule a young man who is a bit soft and shy (it almost equates to 'milquetoast')... the sort of thing an overbearing relative might say to you
"Come on, put your back into it you big girls blouse!"
"You can't drink diet coke in a pub, you big girl's blouse"
"Did you see the way Beckham was rolling around on the grass after that tackle. Big girl's blouse"