how to select all class except the clicked element in JQuery?

Use the not selector.

Example:

$('.collapsiblock').click(function(){
     $('.collapsiblock').not(this).each(function(){
         $(this).slideUp();
     });
     $(this).slideDown();
})

Try this,This is a better way because if you use each function it will load and in the future when you have more than a thousand div it will take a long time to slide up and slide down.

Example:

$('.collapsiblock').click(function(){
   $('.collapsiblock').not(this).slideUp();
   $(this).slideDown();
});

You could keep track of which element has already been clicked with your own jquery click handler and jquery's data(...) function. Then filter iterating your .collapsiblock items with jquery's filter (...) function to include the items you need.