i can't believe you've done this 

Something uttered by British people after they've been suckered punched. Usually preceded by the exclamation "Aw fuck", and accompanied by a look of complete bewilderment.

British guy: Blah Blah Blah Blah
British guy's friend: *punches British guy in the face*
British guy: "Aw FUCK, I can't believe you've done this!"

i can't believe you've done this by Susake December 1, 2007

I Can't Believe You've Done This 

the new meme, originating from the infamous youtube video

http://youtube.com/watch?v=8lBO23Dh23I

pete: hey, say thanks to your mum for me
sam: aw fuck, i can't believe you've done this

I Can't Believe You've Done This by crincled January 8, 2009

ah fuck, I can't believe you've done this. 

A statement of frustration said when one is about to say something and is interrupted abruptly; usually with a punch to the face.

Note: It has to be said in a non-enthusiastic, brittish, calm and polite manner, if you will.

Example:

Some guy: "Hello everyone, i'm here today to talk about... *PUNCHED IN THE FACE*

Same guy: "Ah fuck, I can't believe you've done this."

ah fuck, I can't believe you've done this. by JoãoPaulo November 13, 2007

Ah fuck. I can't believe you've done this. 

Best response to being punched. Ever.

Guy #1: *Punches Guy #2 in the face*
Guy #2: "Ah fuck. I can't believe you've done this."

Ah fuck. I can't believe you've done this. by liMPiNMEdiC January 6, 2008

Ah Fuck I can't believe you've done this 

Expression of anger after someone has annoyed you

"Ah fuck I can't believe you've done this Barry why did you break my mum's lamp."

Ah Fuck I can't believe you've done this by Anti-hypofritz February 26, 2017