(someone) busted out laughing

The phrase "bust out laughing" describes someone suddenly laughing really hard. You "bust out laughing" when something funny and unexpected happens. 

This is a casual and slangy spoken English phrase. The more correct expression is "burst out laughing":

They all burst out laughing at the sight of Emmett in his gorilla costume.

Use "burst out laughing" in more formal and written English.

This phrase appears in these lessons: