Oh boy!

Слово «Boy» присутствует в английском языке с 1300 года.

not to mention

You work at a company that's starting to build applications for tablet computers and phones. You and a group of colleagues are discussing whether to design one layout for all different devices, or separate layouts for each. You just gave one reason why it's better to just use one layout. Now you give another.  Not to mention, there are always new devices coming out.

God only knows

Expressions with the word 'KNOW'

#1 – as far as I know

Use this expression to say that you believe a fact is true… although there is a possibility that you could be mistaken.