Literal translation
to tear oneself apart with laughter
Meaning
to laugh until one can't breathe
Explanation
Laughing until one chokes, literally tearing oneself apart with laughter. The verb estrassa literally means to tear, hence uno estrasso, a rag, which passed into regional French. Figuratively, the reflexive s'estrassa means to cough violently, to choke, as in « Vé ! le petit qui s'estrasse ! », look, the kid is choking. Hence the image of laughter so violent it takes one's breath and brings on coughing, which does happen from laughing hard. The expression is so common that a shortened form, s'estrassa or s'estrasser, is enough to be understood.