set someone off
set
someone
off
cause
someone to
start
doing
something, especially
laughing
or
talking
:
｟英話｠ A〈人〉を泣かせる; 笑わせる; Aに(結局)いつもの話を語らせるはめになる
e.g.
anything will set him off laughing.
#phrasal_verb