When Misao is trying to find Ojiro, she tries to figure out who he is by being the only person who reacts to the word "bakeratta".
He gets very annoyed and because of this she's able to find him.
Why is Ojiro so offended by this word?
I looked it up a bit and found that it's a reference to Obake no Q-Taro, but it still doesn't explain his anger.
It appears one of the main characters of Obake no Q-taro is also called Ojiro.
I thought Q-taro was the one who said "Bakeratta", so I was looking mostly at his character - but it is actually his little brother, Ojiro, who is the link.
He can understand everyone speak, but can only say "Bakeratta", Q-taro is the only one who understands what this means.
So I guess his Ojiro and his brother (in Megane X Parfait) watched it before, and made a joke out of it because they share the name.