To comment in the middle of a conversation.
Michelle: So I went into Wal-Mart and there was a lady in her bikini buying her son a...
Hannah: If she had the audacity...
Michelle: Excuse me?
Hannah: Sorry I was just commentating.
to go on a commenting spree
Bill: I was downtown the other day commenting on stuff for this documentary I'm making
Ted: Dude you were totally commentating!