Lol, sorry, I meant its used like the F bomb. It can be said as a short sharp expletive "Merde!", a long drawn out one "meeeeeeerde", a surprised expletive "oh merde!", you can call something rubbish "C'est de la merde", and even a fatalistic expression "eeeet meeeeerde 😔"
And if you really want to emphasise it, you can exclaim both syllable individually "mer! Deux!".