in this case, the brat is giving enough sign to notice, someone you don't know suddenly appeared out of nowhere and said something nonsensical, why would you bother with someone like that? that's so much waste of time.
if it's me, i would be confused and just say "who are you?" and then leave.
if you know someone you argue with is a stupid person and didn't want to listen to anything from you, then why bother to talk to them? just ignore them.
hah
he is very wise and mature before, but why now he become look like a real high school kid just because of some random brat?
i'am very disappointed.
he could just ignore him like he is not existed but instead he do that