Ah Meng is an alternate name BoBoiBoy
used to call Ying
In Episode 10, BoBoiBoy Lightning accidentally called Ying as Ah Meng which made her upset knowing that it's a guy's name.
Because BoBoiBoy Earthquake doesn't know what Fang's name yet, he called him "You're such a scaredy Ah Meng!!!".
"Hey, Ah Meng is a boy's name!"
"You're such a scaredy cat, Ah Meng!"