when people talk past tense about something that happen(
s/ed) and repeat the word 'do' in a sentence and automatically you think of poop. if you just said do once the sentence would
mean exactly the same thing and may even need fewer words but by adding a do to a
do it makes the focus on
poo which is a specific thing to do, do you think? so it's ok to giggle or laugh or offer a tissue when someone talks and says do do