I was just wondering how "shut up" has come to be used to express extreme shock at something someone says instead of to ask someone to stop talking. I am pretty sure this use of the terms came from American TV as usual and have translated into the same usage by many youngsters in Singapore. As seen in the Mean Girls trailer, when one of the Plastics says "Shut up! Shut up!" at 0:35 and Cady replies "I didn't say anything.", showing very clearly the confusion that might arise when the phrase now carries a new meaning when used in a certain way.
Perhaps the key is in the pronunciation, particularly the tone. If "shut up" is said with a more significant pause in between the two words accompanied with a slower enunciation of the words and eyes opened so big you look like your eyeballs are going to fall out, then it would mean extreme shock instead of the other meaning. It makes it easier if the word "up" is said with a rising tone, a high pitched voice would help in this case, and a meaning of extreme shock would be translated to the other person listening. It seems only girls use "shut up" this way though, given the need for a high pitched voice to successfully evoke the right meaning of the phrase and also because guys just do not react to what their friends say in such extreme manners, if anything shocks them, the fist is what they take out, not the unbelievably awesome phrase "shut up!".
