Jenny, gib mal das 'keyword' bei LEO als Suchbegriff ein und schau Dir auch die Diskussionen zu dem Begriff an, die unterhalb der LEO-Antworten angezeigt werden . . .

(z.B.: related discussion: send someone up - jemanden verarschen
)

@Jenny - I don't think it can be translated very directly (certainly not by me, on a Sunday night after a full day at the computer ;-)
Maybe you can use something else that captures the gist of what the phrase says:
Do you think I'm a complete idiot, or what?! (fairly angry)
You're a big help! (v. sarcastic)
...or something like that.

ok danke für eure Hilfe^^

Das müsste es eigentlich treffen. Any natives around?

Never heard that one before, I assume it is BE only? Doesn't it just express extreme disbelief? Whereas "verarschen" clearly expresses annoyance. Any UK natives in the house?

@Norbert: No, "pull the other leg, etc." does not express extreme disbelief at all. It's equivalent to saying "Just how stupid do you think I am!?", so there's definitely annoyance being conveyed. That said, the expression "pull the other leg, it's got bells on" is a bit dated IMHO and would nowadays be shortened to Pull the other one, the rest of the phrase being implicit.
Another BE expression that occurs to me at the moment is "Do I look like a cabbage?", cabbages being green and "green" meaning "naive" or "stupid".

@Anne(gb): Thanks for elucidating this AE speaker. Two countries divided ...

verarschen kann ich mich selbst / I can fool myself or Let me bullshit myself.

Hi Jenny,
one cannot always translate word for word, English to German. I hope this helps.

Ist aber eher sowas wie "Ich bin doch nicht von gestern" oder so...

I like this suggestion--it is stronger than the others, and I always thought that "verarschen" was a pretty strong word. This seems to be a good match for that.

Hope a further native opinion helps. :)

Dies könnte es am besten treffen.

"Are you taking the piss?" oder "don't take the piss!"
wohl auch eher BE, trifft es aber glaub' ich.

Ich denke das trifft es recht gut :-)

Das ist jedenfalls der Titel eines Songs von "Death by stereo".

Hab mich schon wieder als "incorrect" outen müssen...grrmpf.