Don’t know how to open my mouth..

I overheard this when I was queuing to buy bubble tea.

Daughter: "Mum, I want to drink that, can you help me order?"

Mum: "Just tell the person what you want."

Daughter: "But I don't know how to open my mouth and ask. (我不懂怎么开口讲)"

You know what I told my gf after I heard this? "Then you know how to open your mouth and drink?"

Okay people I know I am mean. =x lol.