Wake me up before you go-go!

Wham!

George Michael's band before he decided to fly solo.

Wham! (pronunciado /uém/)

Just like that, exclamation mark and everything.

The meaning is quite simple, actually.

It's a sound word (onomatopéia) for an impact or heavy blow.

Algo como BLAM!, ou até PÁ! (a interjeição, não a ferramenta) em português!