Hi Gustavo,
This is a actually what is called 'a figure of speech'. There are no actual tits being laughed off. Some people use figures of speech to illuminate a point or make their writing a bit more colourful.
You can learn a little more about them here:
http://grammar.about.com/od/fh/g/Figure-Of-Speech.htm
I know it can be a little tricky for some people grasp, so if you find you are having problems, you can access some information on adult literacy services in Scotland here:
http://www.aloscotland.com/alo/CCC_FirstPage.jsp
I'm sorry to have confused you. Please don't be shy about getting some help with your literacy issues if you feel you need it.
Cheers, mate
MT